A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is composed of semiconductor material with at least 3 terminals for connection to an external circuit. A current or voltage applied to one pair of the transistor''s terminals changes the current by another pair of terminals. Due to  the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, many transistors are packaged individually, but many more are found embedded in integrated circuits.