Field-effect transistor (FET) is an electronic device that uses electric field to control the flow of current. Applying voltage to the gate terminal changes the conductivity between the drain and source terminals, making it a unipolar transistor that operates with a single carrier type. It uses either electrons or holes as charge carriers, but not both simultaneously. FETs typically exhibit high input impedance at low frequencies. Metal-oxide-semiconductor field-effect transistor (MOSFET) is a type of FET.