Power electronics is a technology that uses power semiconductors for power conversion and switching. At first, AC traction railcars began using silicon diode rectifiers in 1960. After that, thyristors prompted development of power electronics technology. As a result, rail-side equipment are now using SVCs (Static Var Compensators) to improve the voltage quality of power source and stabilize the voltage of feeding circuit. GTO thyristors opened an era of induction motor-driven railcars using inverters. Inverters located on the rail-side can also compensate for all kinds of railcar loads. Furthermore, switching technology has put the section arc prevention equipment by shortening the circuit of boosting transformer into practical use. Static changeover switches for Shinkansen are also under development. The development of power semiconductor is in progress. More efficient and compact semiconductors will soon appear for a wide range of applications.