Bipolar Transistors - BJTA bipolar transistor, also known as a BJT (bipolar junction transistor), is a type of transistor that uses both electrons and holes as charge carriers. It is made up of three layers of semiconductor material: the emitter, the base, and the collector. When a voltage is applied to the base, it allows current to flow from the emitter to the collector. Bipolar transistors are used in a variety of applications, including amplifiers, switches, and digital logic circuits. They are known for their high current and voltage gain, making them useful for a wide range of applications.