A programmable read-only memory device comprising a memory cell transistor which has a floating gate and a control gate formed above the floating gate. The programmable read-only memory device further comprises a means for delaying the application timing of a high voltage to the control gate from that of a high voltage to the drain of the memory cell transistor when a data programming operation is performed by applying the high voltage to the control gate and the drain of the memory cell transistor, thereby ensuring reliable a data write operation even at a low programming voltage.