(FET) A transistor with a region of donor material with two terminals called the "source" and the "drain", and an adjoining region of acceptor material between, called the "gate". The voltage between the gate and the substrate controls the current flow between source and drain by depleting the donor region of its charge carriers to greater or lesser extent. There are two kinds of FET's, Junction FETs and MOSFETs. Because no current (except a minute leakage current) flows through the gate, FETs can be used to make circuits with very low power consumption. Contrast bipolar transistor.