Field-effect transistors (FETs) are voltage-controlled devices, while transistors are current-controlled devices. FETs should be chosen when only a small current draw from the signal source is permissible; conversely, transistors should be chosen when the signal voltage is low but a larger current draw is allowed. FETs conduct using majority carriers, hence they are called unipolar devices, while transistors conduct using both majority and minority carriers, hence they are called bipolar devices.
Some FETs have interchangeable source and drain terminals, and their gate voltage can be positive or negative, offering greater flexibility than transistors.
FETs can operate under very low current and low voltage conditions, and their manufacturing processes allow for easy integration of many FETs onto a single silicon chip. Therefore, FETs are widely used in large-scale integrated circuits.
