Field-effect transistors (FETs) are voltage-controlled semiconductor devices that rely on an electric field to control the shape and conductivity of a channel in the semiconductor material. The basic principle of FETs involves three terminals - the gate, source, and drain - where a voltage applied to the gate controls the current flow between the source and drain terminals. There are two main types of FETs: junction FETs (JFETs) which have a doped semiconductor channel, and metal-oxide-semiconductor FETs (MOSFETs) which use a metal gate separated from the channel by an oxide layer. FETs can be used for switching, amplifying signals, and as variable resistors

1. Field-Effect Transistors