SECS/GEM SEMI Standards Overview

The Generic Model for Communications and Control Of Manufacturing Equipment (GEM) standard is maintained and published by the non-profit organization Semiconductor Equipment and Materials International (SEMI). Generally speaking, the GEM standard defines messages, state machines and scenarios to enable factory software to control and monitor manufacturing equipment. The GEM standard is formally designated and referred to as SEMI standard E30, but frequently simply referred to as the GEM or SECS/GEM standard. GEM intends "to produce economic benefits for both device manufacturers and equipment suppliers..." by defining "... a common set of equipment behavior and communications capabilities that provide the functionality and flexibility to support the manufacturing automation programs of semiconductor device manufacturers" [SEMI E30, 1.3]. SECS/GEM is a standard implementation of the SECS-II standard, SEMI standard E5.

Many different types of equipment in semiconductor (front end and back end), surface mount technology, electronics assembly, photovoltaic, LED, flat panel display and other manufacturing industries worldwide provide a GEM interface on the manufacturing equipment so that the factory host software can communicate with the machine for monitoring and/or controlling purposes. Because the SECS/GEM standard was written with very few semiconductor-specific features, it can be applied to virtually any manufacturing equipment in any industry.

Download Cimetrix's White Paper on the SEMI SECS/GEM Standards.

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Industrial Usage of the SECS/GEM Standard

All GEM compliant manufacturing equipment share a consistent interface and certain consistent behavior. GEM equipment can communicate with a GEM capable host using either TCP/IP (using the HSMS standard, SEMI E37) or RS-232 based protocol (using the SECS-I standard, SEMI E4).  Each equipment can be monitored and controlled using a common set of SECS-II messages specified by SECS GEM. When an equipment has a GEM interface, it takes just minutes (or even seconds) for factory GEM host software to establish communication and begin monitoring the machine's activity. This means that equipment manufacturers can spend more time and money improving the machine's quality by providing a common interface to all factories. Furthermore, factories can spend more time and money improving production and processes, rather than setting up communication to the machines.

There are many additional SEMI standards and factory specifications that reference the SECS/GEM standard. These additional standards are either industry-specific or equipment-type specific. Following are a few examples.

  • Semiconductor Front-End

    The semiconductor front-end industry defined a series of standards known as the GEM300 standards that include SEMI standards E40, E87, E90, E94, E116E148, and E157. and also references the E39 standard. Each standard provides additional features to the GEM interface yet build upon the features in GEM E30 standard.

    300 mm factories worldwide use the underlying SECS/GEM standard's data collection features in order to monitor specific equipment activity such as wafer movement and process job execution.

    The SECS/GEM standard and the additional GEM 300 standards are required on nearly each and every 300mm wafer manufacturing tool in order to implement the manufacturing automation. This industry has been the strongest supporter of the GEM and related SEMI standards. Read more about the GEM300 standards in the SEMI GEM 300 Connectivity Standards introduction.

  • Semiconductor Back-End

    Numerous equipment in the Semiconductor Back-End industry implement the SECS/GEM standard. Additional standards have been implemented such as SEMI E122 STANDARD FOR TESTER SPECIFIC EQUIPMENT MODEL and SEMI E123 STANDARD FOR HANDLER EQUIPMENT SPECIFIC EQUIPMENT MODEL.

  • Flat Panel Display

    The Flat Panel Display industry has largely been a long-time user of SEMI standards for connecting manufacturing equipment to their factory information and control systems, but the interfaces are typically user-specific and incorporate custom SECS messages.

    As panel sizes and feature counts continue to increase (consider the large LED-based high-definition televisions), the FPD industry will undoubtedly make use of more and more manufacturing data to maintain product quality and manufacturing efficiency.

  • Surface Mount Technology

    Many equipment in the Surface Mount Technology industry support the SECS/GEM standard, including chip placement, solder paste, oven and inspection equipment. The GEM standard has been used on these equipment for over 15 years.

  • Photovoltaic

    In 2008, the Photovoltaic industry officially decided to adopt the SECS/GEM standard and submitted a proposal for a new SEMI standard, ballot 4557, as a new PV industry standard. Even prior to adopting the SECS/GEM standard, several photovoltaic equipment suppliers already were capable of supporting the GEM/SECS standard. The new standard is called the "GUIDE FOR PV EQUIPMENT COMMUNICATION INTERFACES (PVECI)" and defines a framework that utilizes the SEMI E37 (HSMS), SEMI E5 (SECS-II), SEMI 30 (GEM), SEMI E148 and SEMI E10 standards.

  • High-Brightness LEDs

    The High-Brightness LED industry is currently working with SEMI to define needed standards through the HBLED Task Force.  The adoption of GEM has been accepted and further investigation is taking place concerning the GEM 300 and EDA (Equipment Data Acquisition) standards.

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SECS/GEM Host and GEM Equipment Communication

In a factory SECS GEM implementation there are two parties, the host and equipment. The equipment runs GEM interface software on one of its computers that must implement and comply with the SEMI standards. The manufacturer (factory) runs GEM host software that establishes communication with the equipment's GEM interface. A host is also called a station controller or line manager. Often the host software is part of the factory's Manufacturing Execution System (MES). A host system can communicate with one or multiple equipment GEM interfaces at the same time. The host communicates directly with each equipment using either the SEMI E4 SECS-I standard (RS-232 based serial communication) or SEMI E37.1 HSMS-SS standard (TCP/IP based network communication). Certainly the HSMS-SS standard is more appropriate and convenient for today's modern factories and is therefore used almost exclusively in modern factories.

A host does not have to comply with the SECS/GEM standard since the standards only set equipment expectations; however in order to make use of the GEM interface a host must implement the host-side of the communication. The SECS/GEM standards set clear equipment behavior expectations for each possible host message.

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SECS/GEM Feature Summary

The SECS/GEM standard's key features are described in the following paragraphs. Minimal GEM compliance requires only a small set of these features to be supported since many of the features described are optional, additional capabilities. Many of the features have state models to clearly define states, sub-states and transitions between states. The state models make GEM interface implementations consistent and predictable.

The SECS GEM standard defines a number of SECS-II messages scenarios; an ordered sequence of SECS-II message transactions. The SECS-II message scenarios establish an implementation guideline so that the equipment manufacturer can anticipate how the host might use the SECS/GEM standard.


The GEM SECS standard defines how an equipment and host initially establish communication. It also defines how communication is re-established when communication is broken. An on-line identification method verifies the equipment's hardware and software identity. Terminal service features allow the host operator and equipment operator to exchange text manually typed at a console.


The GEM/SECS standard outlines a control state model to define the level of cooperation between the host and equipment operator. GEM Equipment provide three basic levels of host control which determine the host's ability to control and monitor the equipment. The equipment operator sets the level of host control.

Remote control capabilities permit the host to send GEM-defined commands like "START", "STOP", "PAUSE", "RESUME", and "ABORT" to control the equipment's processing. The equipment can define additional custom commands. Each command can have one or more arguments with data to clarify the command.

Equipment constant features allow the host to set and retrieve equipment constant values which govern the equipment's behavior. GEM requires a small set of equipment constants to configure the GEM state machines. An equipment can define additional equipment constants to allow the host to configure any aspects of the equipment behavior.

Operation Notification

Collection events and alarms allow the host to monitor the interesting equipment operation. Equipment collection events notify the host of significant normal and abnormal activity. Equipment alarms notify the host when potentially dangerous activity is detected and cleared. The host determines which collection events and alarms are setup for notification. The equipment sends SECS-II messages to the host only for the events and alarms that are enabled for notification. This minimizes communication traffic on the network. Certain events are required by the SECS GEM standard, but the equipment is expected to define additional events to allow the host to monitor the equipment-specific activities.

Data Gathering

SECS/GEM defines six methods of gathering data. The host can gather data from the equipment, but an equipment cannot gather data from the host.

  1. A set of status variable values can be requested at any time.
  2. A set of equipment constant values can be requested at any time.
  3. A report containing status variable, data variable, and equipment constant values can be requested at any time.
  4. A host can define reports and attach them to collection events so that the report data is transmitted along with the collection event in the same SECS-II message. This feature enables data to be sent to the host as the values become available thereby reducing the host's obligation to poll information. This event report data collection also enables the host to gather the data related to each event.
  5. The host can define traces so that the equipment periodically transmits the specified status variable values at a set interval. This feature enables the host to poll the equipment status without having to ask the data at each interval.
  6. The host can configure limits monitoring so that the equipment notifies the host whenever a specified variable value transitions across a host-defined limit boundary. This feature eliminates the need for the host to poll critical values is situations where the host is only concerned when the value becomes too high or low. Multiple limit boundaries can be defined.

Process Program (Recipe) Management

A process program "is the set of instructions, settings, and parameters under control of the equipment that determine the processing environment seen by the manufactured object" (SEMI E30, Process program management features include the following:

  • Host can download a process program to the equipment for storage on the equipment.
  • Host can query a process program from the equipment for storage on the host.
  • Host can delete a process program on the equipment.
  • Host can request a list of available process programs.
  • Equipment operator can send a process program to the host.
  • Equipment operator can request a process program from the host.
  • Host can select a process program for execution using a PP-SELECT remote command
  • Equipment will notify the host when a process program is created, edited, deleted, or selected by the equipment operator.


Spooling capabilities provide the means for the equipment to queue information intended for the host during communication failure. When communication is restored, the host can purge or request the queued data. The host can configure which information is queued, how a full queue is handled, the queue size, and how queued information is recovered. The host can also switch spooling features on or off.


The SECS/GEM standard requires that each equipment provide a GEM interface manual. It must include a GEM compliance statement, complete SECS-II message documentation, complete GEM state model documentation, and a description of all equipment variables, alarms, collection events, equipment constants, and remote commands.

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Frequently Asked Questions

Where can I get a copy of the SECS/GEM standard?
Official copies must be obtained through SEMI. SEMI offers excellent internet services at their website. Standard documents can be ordered or downloaded for a fee at the SEMI website
How does a system become GEM certified?
There is no official SECS GEM certification. GEM compliance is self proclaimed. Software programs are available for testing GEM Equipment such as TESTConnect and SECSConnect. Note that GEM compliance does not require all GEM/ SECS features to be implemented. For example, some equipment do not implement remote commands and process program management yet they can still be GEM compliant if the correctly implement the GEM Fundamental Capabilities.
Can more than one host establish communication with an equipment at one time?
Not in many GEM interfaces. However, the Cimetrix CIMConnect software product has a built-in multiple client (multi-host) feature that inherently makes it trivial to communicate with more than one SECS/GEM host at a time using HSMS-SS or SECS-I communication. When using HSMS-SS, each client uses a unique port.
How long does it take to implement a GEM SECS interface?
If building the GEM SECS software from scratch, it can take a few man years to develop software that will be reliable in a variety of factories. It is much more cost effective to purchase a commercial software product. There are a couple commercial SECS/GEM software products available such as the CIMConnect product available from Cimetrix which many consider to be the best product on the market.
How fast is a GEM/SECS interface?
Current versions of the SECS GEM standard allow the host to setup trace data collection with the message rate specified in milliseconds. In practice, some factories request data at rates of about 10Hz, or 1 set of data every 100ms. Because the SECS-II and HSMS message format is very efficient, a lot of data can be transferred using little network bandwidth. The precise data rates depend on many factors such as the network, the GEM software in both the host and equipment systems, and the computer hardware. Older versions of the SECS/GEM standard were limited to 1 Hz trace data collection.
What features in a SECS/GEM product are important?
There are many important features, but here are some of the key ones:
  • Customer Support
    The GEM interface can be a production-critical feature. There are many details in the GEM SEMI standards that take years to master. Before selecting a product, make sure that the product is backed by a solid company with a responsive, experienced customer support team.
  • Performance

    Some products use much less CPU than others for the same set of tasks. A product that uses less CPU can achieve higher data collection requirements. As factories attempt manufacturing process optimization, they rely on more and more data collection from the equipment. Select a product that can use computer resources most efficiently and can meet both today's and tomorrow's throughput requirements.

  • Multiple Client Support

    In recent years, the importance for supporting multiple clients has increased. For example, PV manufacturers documented the need for an "IT interface of the equipment that allows an arbitrary number of clients to connect to the equipment in order to gather data from the equipment (all kinds of data collection) and to interact with the equipment (remote control, etc)". Choose a product that has multiple client access as a built-in feature such as CIMConnect.

  • Client Server Architecture

    A GEM interface interacts with all of the components within the equipment. Purchase a product with a client-server architecture so that all of the components can interact directly with the SECS GEM software. This saves on software development.

Can changes be made to the SECS/GEM standard?
The SECS/GEM standard is an active SEMI standard managed by the GEM 300 task force. Periodically changes to the GEM SECS standard are submitted for discussion and for ballot approval. Changes must be approved according to SEMI's standard processes. Anyone can join the GEM 300 task force, vote on the changes to the standard, and submit recommendations. More information is available from the following websites:
Where can I ask questions about the SECS/GEM standard?
You are welcome to emails questions to Also, there is an industry forum located at this website Equipment Integration and Automation Standards Discussion
How much network bandwith does a GEM interface require?
While the equipment determines how much information is available to the host, ultimately the host determines the bandwidth utilization by enabling the desired collection events and alarms and by disabling the undesired ones. The host also determines the amount and frequency of data gathering, recipe management, remote commands, and other features. If all of the events and alarms are disabled, then a GEM interface connection will be nearly silent.


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SECS/GEM Terminology

An alarm is related to any abnormal situation on the equipment that may endanger people, equipment, or material being processed" [SEMI E30, 2]. GEM allows the host to be notified when alarm conditions are detected and cleared.
Collection Event
A collection event is a "detectable occurrence significant to the equipment" that "is considered to be significant to the host". [SEMI E30, 2] GEM allows the host to be notified when a collection event occurs. This allows the host to track the equipment's activity.
Data Variable
Data variables "…may only be valid upon the occurrence of a particular event". [SEMI E5, 6.6]. The host can gather data variable values from the GEM Equipment. The data variable values provide information specifically related to the event.
Equipment Constant
Equipment Constants are "settable by the Host"[SEMI E5 6.6]. The host can gather equipment constant values from the GEM Equipment. The host can also set equipment constant values on the GEM Equipment to control the equipment's behavior.
GEM Equipment
An "intelligent system which communicates with a host" [SEMI E4, 2.1] and complies to the SECS/GEM standard.
"An intelligent system which communicates with the equipment." [SEMI E4, 2.1]. The host can be viewed as a line management system. GEM does not intend to define how the host should behave. The GEM SECS standard defines the set of messages a host must use when interacting with GEM Equipment. A GEM Equipment can communicate with one host. A host can communicate with multiple GEM Equipment.
SEMI standard High Speed Message Service-Single Session which defines TCP/IP network communication used by SECS/GEM for host/equipment communication. It is replacing the SECS-I standard. Only one client host can use a specific port at a time.
GUIDE FOR PV EQUIPMENT COMMUNICATION INTERFACES (PVECI), based on SECS/GEM, specifically for photovoltaic equipment suppliers.
Process Program
A Recipe (see Recipe)
A set of instructions for the equipment.
"A set of variables predefined by the equipment or defined by the host…". The host uses reports to gather status variable, data variable, and equipment constant values. The host can request a report explicitly or attach a set of reports to a collection event.
Status Variable
"Status variables may include any parameters that can be sampled in time such as temperature or quantity of a consumable." [SEMI E5, 6.5] "Status values … always contain valid information." [SEMI E5, 6.6]. The host can gather status variable values from the GEM Equipment.
SEMI Equipment Communications Standard 1 Message Transfer - defines RS-232 serial communication used by SECS GEM for host/equipment communication. It is phasing out due to inherent speed limitations. It is being replaced by the HSMS standard.
SEMI Equipment Communications Standard 2 Message Content. SECS GEM is a specific implementation of the SECS-II standard. SECS-II defines most concepts and functionality used in the SECS/GEM standard. Many SECS-II capable systems are not GEM compliant.
SECS-II Message
All GEM Equipment and host communication is accomplished using SECS-II messages. Each unique SECS-II message is identified by its stream number (S) and function number (F). The SECS-II standard defines a large set of SECS-II messages determining each one's purpose, content, and usage. The SECS GEM standard defines how to use a subset of these SECS-II messages yet allows other SECS-II messages to be used in addition to this subset.

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