The device is one of the basic building blocks of modern electronics.^[1] It is composed of semiconductor material, usually with at least three terminals for connection to an electronic circuit. A voltage or current applied to one pair of the transistor’s terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power,this device can amplify a signal. Some of this devices  are packaged individually, but many more are found embedded in integrated circuits.

Most of this device are made from very pure silicon, and some from germanium, but certain other semiconductor materials are sometimes used and this device may have only one kind of charge carrier, in a field-effect , or may have two kinds of charge carriers in bipolar junction transistor devices but with the vacuum tube, Most of this device are generally smaller and require less power to operate. Certain vacuum tubes have advantages over transistors at very high operating frequencies or high operating voltages. Many types of this device are made to standardized specifications by multiple manufacturers.

this device as an amplifier

The common-emitter amplifier is designed so that a small change in voltage (V_in) changes the small current through the base of the transistor whose current amplification combined with the properties of the circuit means that small swings in V_in produce large changes in V_out.

Various configurations of single transistor amplifiers are possible, with some providing current gain, some voltage gain, and some both.

The first discrete-transistor audio amplifiers barely supplied a few hundred milliwatts, but power and audio fidelity gradually increased as better transistors became available and amplifier architecture evolved.Modern transistor audio amplifiers of up to a few hundred watts are common and relatively inexpensive.