Then we can define the saturation region or “ON mode” when using an e-MOSFET as a switch as gate-source voltage, VGS > VTH and ID = Maximum. For a P-channel enhancement MOSFET, the Gate potential must be more negative with respect to the Source.
By applying a suitable drive voltage to the gate of an FET, the resistance of the drain-source channel, RDS(on) can be varied from an “OFF-resistance” of many hundreds of kΩ’s, effectively an open circuit, to an “ON-resistance” of less than 1Ω, effectively a short circuit.
When using the MOSFET as a switch we can drive the MOSFET to turn “ON” faster or slower, or pass high or low currents. This ability to turn the power MOSFET “ON” and “OFF” allows the device to be used as a very efficient switch with switching speeds much faster than standard bipolar junction transistors.