A transistor is a semiconductor, differentiated from a vacuum tube primarily by its use of a solid, non-moving part to pass a charge. Transistors are crucial components in virtually every piece of modern electronics, and are considered by many to be the most important invention of the modern age (as well as a herald of the Information Age).

The development of the transistor grew directly out of huge advances in diode technology during World War II. In 1947, scientists at Bell Laboratories unveiled the first functional transistor, after a number of false starts and technological stumbling blocks.

The first important use of the transistor was in hearing aids, by military contractor Raytheon — inventors of the microwave oven and producer of many widely-used missiles, including the Sidewinder and Patriot missiles.

The first transistor radio was released in 1954 by Texas Instruments, and by the beginning of the 1960s transistor radios had become a mainstay of the worldwide electronics market. Also in the 1960s transistors were integrated into silicon chips, laying the groundwork for the technology that would eventually allow personal computers to become a reality. In 1956, Bill Shockley, Walter Brattain, and John Bardee won the Nobel Prize for physics for their development of the transistor.

The primary type of transistor in use is known as a bipolar junction transistor, which consists of three layers of semi-conductor material, two of which have extra electrons, and one which has gaps in it. The two with extra electrons (N-Type) sandwich the one with gaps (P-Type). This configuration allows the transistor to be a switch, closing and opening rapidly like an electronic gate, allowing voltage to pass at a determined rate. If a bipolar transistor is not shielded from light, the light may be used to open or close the gate, in which case it is referred to as a phototransistor, functioning as a highly-sensitive photodiode.

The secondary type of transistor is known as a field-effect transistor, and consists either entire of N-Type semi-conductive material or P-Type semi-conductive material, with the current controlled by the amount of voltage applied to the transistor.