MOS Controlled Thyristor (or MCT) is voltage controlled fully controllable thyristor. The MCT is similar in operation with GTO thyristor, but it has voltage controlled insulated gate. It has two MOSFETs in its equivalent circuit. One is responsible for turn-on and the another is responsible for turn-off. A thyristor with only one MOSFET in its equivalent circuit, which can only be turned on (like normal SCRs), is called a MOS Gated Thyristor.
Positive voltage on the gate terminal with respect to the cathode turns the thyristor to the on state.
Negative voltage on the gate terminal with respect to the anode, which is close to cathode voltage during the on state, turns the thyristor to the off state.