Metal-Oxide-Semiconductor Field-Effect Transistor, a type of field-effect transistor (FET). MOSFETs have an insulated gate, the voltage of which determines the conductivity of the device. This can be used for amplifying or switching electronic signals. (From: Wikipedia)

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: