A program lock circuit for inhibiting programming of memory cells. A memory array can have both mask programmable and one-time programmable memory cells connected to the wordlines and the bitlines. Since the one-time programmable memory cells are convertible into mask programmable memory cells through mask programming, such as diffusion mask programming or contact/via mask programming, these mask programmed cells are still electrically programmable, thereby destroying the originally stored data. The programming lock circuit inhibits programming of the mask programmed cells by detecting an activated wordline during a programming operation, and then immediately disabling or decoupling the high voltage supply that is provided to the wordline drivers. Mask programmed transistor elements coupled to each wordline detect the wordline voltage and disable the high voltage supply. A mask programmable master lock device can be provided to inhibit all the rows in the memory array from being programmed.