only its external power circuit, but also the signal on its driving terminal (this terminal is known as the gate or base).
* A four-terminal device (e.g. Silicon Controlled Switch - SCS). SCS is a type of thyristor having four layers and four terminals called anode, anode gate, cathode gate and cathode. the terminals are connected to the first, second, third and fourth layer respectively.

Another classification is less obvious, but has a strong influence on device performance:
* A majority carrier device (e.g., a Schottky diode,