An MOS-controlled thyristor (MCT) is a voltage-controlled fully controllable thyristor, controlled by MOSFETs. It was invented by V.A.K. Temple in 1984, and was principally similar to the earlier insulated-gate bipolar transistor (IGBT). MCTs are similar in operation to GTO thyristors, but have voltage controlled insulated gates. They have two MOSFETs of opposite conductivity types in their equivalent circuits. One is responsible for turn-on and the other for turn-off. A thyristor with only one MOSFET in its equivalent circuit, which can only be turned on, is called an MOS-gated thyristor.