A semiconductor switch comprises a PNPN structure arranged to provide an SCR-like functionality, and a MOS gate structure, preferably integrated on a common substrate. The switch includes ohmic contacts for the MOS gate, and for the cathode and gate regions of the PNPN structure; the anode contact is intrinsic. A fixed voltage is typically applied to an external node. The MOS gate structure allows current to be conducted between the external node and the intrinsic anode when on, and the PNPN structure conducts the current from the anode to the cathode when an appropriate voltage is applied to the gate contact. Regenerative feedback keeps the switch on once it begins to conduct. The MOS gate inhibits the flow of current between the external node and anode—and thereby turns off the switch—when off. When on, the MOS gate's channel resistance serves as a ballast resistor.