Field-Effect Transistor:

The field-effect transistor that is abbreviated as FET relies on an electric field to control the shape and therefore the conductivity of a channel of one sort of charge carrier in a semiconductor material. FETs are occasionally termed as unipolar transistors to contrast their single-carrier-type operation along with the dual-carrier-type operation of bipolar junction transistors that is abbreviated as BJT. The idea of the FET predates the BJT, even though it was not physically implemented until after BJTs because of the limitations of semiconductor materials and the relative easiness of manufacturing BJTs as compared to FETs at the time.