(abbreviated as SCR) is a high-power switching device with a four-layer (PNPN) semiconductor structure, hailed as the “cornerstone of switching” in the field of power electronics. It has three electrodes: anode (A), cathode (K), and gate (G).

      A bidirectional thyristor (TRIAC) can conduct in both directions, making it suitable for AC voltage regulation and contactless switching; Gate Turn-Off Thyristors (GTOs) and Integrated Gate Commutated Thyristors (IGCTs) address the limitation of not being able to turn off via the gate and are used in high-voltage frequency conversion and rail transit; in addition, there are fast thyristors suitable for high-frequency circuits and light-triggered thyristors (LTTs), the latter of which are commonly used in high-voltage direct current transmission (HVDC).