The transistor is an electronic device that has the function of amplifying current. It consists of three electrodes, namely the emitter, base, and collector. When a positive voltage is applied to the base, the collector junction is forward-biased, forming an emitter junction; conversely, when a negative voltage is applied to the collector, the collector junction is reverse-biased, forming a drain-source junction. The transistor is one of the most important passive components in electronic devices, usually represented by "v" (positive) and "g" (negative) in circuits, with the symbol "d" and the unit of pf (farad).

In semiconductor devices, the transistor is the most common device and the most widely used among all basic semiconductor components. Its basic structure is very simple, mainly composed of three parts: the base region, collector, and emitter, channel, and depletion region. The transistor's high working frequency, small size, low power consumption, good dynamic characteristics, stability, low noise, large temperature coefficient, long life, strong radiation resistance, and high reliability make it widely used in the electronic field.

According to the shape, transistors can be divided into planar transistors, rectangular transistors, and field-effect transistors. According to its use, it can be divided into ordinary power transistors, high-frequency power transistors, ultra-high-frequency power transistors, and special power transistors. According to the manufacturing process, it can be divided into double-diffusion silicon double-base type, double-diffusion aluminum double-base type, unidirectional thyristor, polycrystalline thyristor, gate array, and other types. Different special diodes and transistors with different structures and functions can be produced according to different application scenarios and requirements.

Transistors are mainly used in rectifiers, voltage regulators, oscillators, and other circuits. Its working principle is to change the output signal's size by controlling the current size of the three terminals.