bipolar junction transistor abbr., BJT (rus. транзистор, биполярный otherwise полупроводниковый триод) — Three-electrode semiconductor device, a type of transistors. In a bipolar (from bi meaning two) transistor, in contract to its other types, the main carriers are both electrons and holes.


Bipolar transistor electrodes are connected to a transistor’s main functional parts, which are three consecutive semiconductor layers with alternating types of impurity conduction. The middle layer is called the base, one side layer is called the emitter, the other is a collector. By layer alternation, npn or pnp transistors are distinguished (n, meaning negative, an electronic type of impurity conduction; p is positive, hole type). The most important operational condition for the transistor is the very small thickness (less than a micrometre) of the middle layer, the base region, and the small concentration of impurity atoms in it. Bipolar transistors are used primarily for the amplification, generation, and transformation of continuous and pulsed electrical signals in the radio- and microwave frequency bands.


  • Naymushina Daria A.
  • Soldatov Eugene S.


  1. Bipolar junction transistor // Wikipedia, the free Encyclopedia. — (reference date: 12.12.2011).