A transistor is a semiconductor device that is employed to amplify and switch electronic signals. It is made up of a solid piece of semiconductor material, with minimum three terminals for connection to an external circuit. A voltage / current applied to one pair of terminals of the transistor changes the current flowing via another pair of terminals. Since the controlled (output) power can be more than the controlling (input) power, the transistor provides amplification of a signal. Nowadays, some transistors are packaged individually, but much more are found embedded in integrated circuits.
The transistor is the basic building block of current electronic devices and is everywhere in modern electronic systems. Following its release in the early 1950s century the transistor revolutionized the field of electronics, and paved the way for smaller and much low-priced radios, calculators, and computers, amongst other things.