In the microelectronics industry, a semiconductor fabrication plant (commonly called a fab; sometimes foundry) is a factory for semiconductor device fabrication.

Fabs require many expensive devices to function. Estimates put the cost of building a new fab over one billion U.S. dollars with values as high as $3–4 billion not being uncommon. TSMC invested $9.3 billion in its Fab15 300 mm wafer manufacturing facility in Taiwan. The same company estimations suggest that their future fab might cost $20 billion. A foundry model emerged in the 1990s: Foundries that produced their own designs were known as integrated device manufacturers (IDMs). Companies that farmed out manufacturing of their designs to foundries were termed fabless semiconductor companies. Those foundries, which did not create their own designs, were called pure-play semiconductor foundries.

The central part of a fab is the clean room, an area where the environment is controlled to eliminate all dust, since even a single speck can ruin a microcircuit, which has nanoscale features much smaller than dust particles. The clean room must also be damped against vibration to enable nanometer-scale alignment of machines and must be kept within narrow bands of temperature and humidity. Vibration control may be achieved by using deep piles in the cleanroom's foundation that anchor the cleanroom to the bedrock, careful selection of the construction site, and/or using vibration dampers. Controlling temperature and humidity is critical for minimizing static electricity. Corona discharge sources can also be used to reduce static electricity. Often, a fab will be constructed in the following manner: (from top to bottom): the roof, which may contain air handling equipment that draws, purifies and cools outside air, an air plenum for distributing the air to several floor-mounted fan filter units, which are also part of the cleanroom's ceiling, the cleanroom itself, which may or may not have more than one story, a return air plenum, the clean subfab that may contain support equipment for the machines in the cleanroom such as chemical delivery, purification, recycling and destruction systems, and the ground floor, that may contain electrical equipment. Fabs also often have some office space.

The clean room is where all fabrication takes place and contains the machinery for integrated circuit production such as steppers and/or scanners for photolithography, in addition to etching, cleaning, doping and dicing machines. All these devices are extremely precise and thus extremely expensive. Prices for most common pieces of equipment for the processing of 300 mm wafers range from $700,000 to upwards of $4,000,000 each with a few pieces of equipment reaching as high as $340,000,000 each (e.g. EUV scanners). A typical fab will have several hundred equipment items.