Goseeko blog

What is a MOSFET?

by Team Goseeko
  • The MOSFET (Metal Oxide Semiconductor Field Effect Transistor) transistors are used for switching and amplification. 
  • This is fabricated in a single chip and is an important device used in electronics.
  • The MOSFET consists mainly of three terminal source(S), gate (G) and drain (D) terminals.
  • It is like FET with three terminals and can be used in analog as well as digital circuits.


  • Also the channel width of the MOSFET varies with the flow of the charge carriers and this is the phenomenon behind its working.
  • Through the source terminal the carriers enter the channel and flow towards the drain.
  • Then the gate terminal controls the channel width.
  • It is insulated from the channel near an extremely thin layer of metal oxide.


1. Depletion Mode

There is maximum flow of charge carriers when there is no voltage on the gate terminal. When voltage of any polarity is applied at the gate terminal the conductivity decreases.

2. Enhancement Mode

The device does not conduct when there is no voltage on the gate. As the voltage increases on the gate, the better the device can conduct.

Working of MOSFET

  • The device functions as a switch as the voltage and flow of current between the source and drain can be controlled. 
  • The MOS capacitor is the main part of MOSFET.
  • Then semiconductor surface at the below oxide layer is located between source and drain terminal. It can be inverted from p-type to n-type by applying positive or negative gate voltages respectively.
  • The holes present in the oxide layer are repelled and move down with the substrate when a positive gate voltage is applied.
  • Then the depletion region that has the negative charges is the acceptor atom. The positive voltage also attracts electrons. So, if a voltage is applied between the drain and source, the current flows between the source and drain and the gate voltage controls the electrons in the channel.

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