The bipolar transistor was a revolutionary invention in the history of electronics, and its inventors, William Shockley, John Bardeen and Walter Bratton, were awarded the 1956 Nobel Prize in Physics.

The work of this transistor involves the flow of both electron and hole carriers, so it is called bipolar, so it is also called bipolar carrier transistor. This mode of operation is different from unipolar transistors such as field effect tubes, which only involve the drift of a single type of carrier. The boundary between the aggregation regions of two different dopants is formed by PN junction.

The charge flow in a bipolar transistor, which is made of three semiconductors with different doping degrees, is mainly due to the carrier diffusion and drift motion at the PN junction. In the case of NPN transistors, electrons in the highly doped emitter region are designed to travel to the base through diffusion. In the base region, the holes are the majority carriers and the electrons are the minority carriers. Because the base region is very thin, these electrons reach the collector through drift motion, thus forming a collector current, so the bipolar transistor is classified as a minority carrier devi.

Bipolar transistors can amplify signals, and has good power control, high-speed work and durability, so it is often used to form amplifier circuits, or drive loudspeakers, motors and other equipment, and is widely used in aerospace engineering, medical devices and robots and other applications.