A field-effect transistor (FET) is a type of semiconductor device that controls the flow of electrical current. It uses an electric field to influence the conductivity of a channel, allowing it to switch or amplify signals. FETs are widely used in electronic circuits due to their efficiency and ability to operate at low power levels. There are several types of FETs, including MOSFETs (metal-oxide-semiconductor FETs) and JFETs (junction FETs). These devices are essential components in various applications, such as computers, amplifiers, and radio transmitters, making them crucial for modern electronics.