A transconductance (using voltage to control current) electronic component used for switching and amplification. Acronym for Metal-Oxide-Semiconductor Field-Effect Transistor. (from [Wikipedia](http://en.wikipedia.org/wiki/Transistor)
A MOSFET is a three-terminal device which is used to control current flow in a circuit. The amount of current allowed to flow between drain and source is proportional to the voltage applied to the gate of the device.
This is a major difference from a conventional bipolar junction transistor; the BJT collector-emitter current is controlled by the base current, while the MOSFET drain-source current is controlled by the gate voltage.
The physical construction of a MOSFET creates a parasitic diode between drain and source, which must be taken into account when designing MOSFET circuits.
Major classifications of MOSFETs:
- Enhancement mode or depletion mode
- N-channel or P-channel
Depletion P-channel MOSFETs aren't used.
They are more often used as switches than as amplifiers.
Further reading:
- Field Effect Transistors in Theory and Practice, Freescale (now: NXP) application note
- Power MOSFET basics, IR application note
