A transistor is a semiconductor device used to amplify or switch electrical signals and power. It is one of the basic building blocks of modern electronics. 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, a transistor can amplify a signal. Some transistors are packaged individually, but many more in miniature form are found embedded in integrated circuits. Because transistors are the key active components in practically all modern electronics, many people consider them one of the 20th century's greatest inventions.
Size comparison of bipolar junction transistor packages, including (from left to right): SOT-23, TO-92, TO-126, and TO-3
Julius Edgar Lilienfeld proposed the concept of a field-effect transistor in 1925.
John Bardeen, William Shockley, and Walter Brattain at Bell Labs in 1948; Bardeen and Brattain invented the point-contact transistor in 1947 and Shockley invented the bipolar junction transistor in 1948.
A replica of the first working transistor, a point-contact transistor invented in 1947
A semiconductor device is an electronic component that relies on the electronic properties of a semiconductor material for its function. Its conductivity lies between conductors and insulators. Semiconductor devices have replaced vacuum tubes in most applications. They conduct electric current in the solid state, rather than as free electrons across a vacuum or as free electrons and ions through an ionized gas.
Outlines of some packaged semiconductor devices
NASA's Glenn Research Center clean room
A stylized replica of the first transistor
