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A junction field effect transistor (JFET) is the the simplest type of three-terminal semiconductor transistor. JFETs are widely employed as electronically controlled switches, voltage-controlled resistors and amplifiers. The semiconductor material in a JFET is positively and negatively doped and arranged to form a channel for effective functioning of the device.
In a JFET, the semiconductor doped with donor impurities forms an n-type channel, whereas a semiconductor doped with acceptor impurities forms a p-type region. An electrical connection at the end of the channel on a JFET is either a drain terminal or source terminal, and the middle terminal is known as a gate. These terminals are actually p-n junctions with the main channel. The main difference between any bipolar junction transistor (BJT) and a JFET is how they are controlled — a BJT is controlled by current, while a JFET is controlled by voltage.