Transistors are the cornerstone of modern electronics. They are core semiconductor devices with functions of signal amplification, current/voltage control and circuit switching, which have completely revolutionized the design and application of electronic circuits. They are mainly divided into two major categories: current-driven Bipolar Junction Transistors (BJTs) and voltage-driven Field-Effect Transistors (FETs, including MOSFETs, JFETs, etc.), as well as composite power transistors (such as IGBTs) that combine the advantages of both. Transistors feature small size, low power consumption, high reliability and easy large-scale integration. They are the fundamental components of all digital circuits (such as CPUs and memories) and analog circuits (such as amplifiers and power supplies), and are widely used in all electronic fields including consumer electronics, communications, automobiles, industry and aerospace.