A
transistor is a
semiconductor device used to
amplify or
switch electronic signals and
electrical power. It is composed of
semiconductor material with at least three terminals for connection to an external circuit. A voltage or
current applied to one pair of the transistor's terminals changes the current through another pair of terminals. Because the controlled (output)
power can be higher than the controlling (input) power, a transistor can
amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in
integrated circuits.