PURPOSE: To increase the set margin of the electrostatic breakdown of an oxide film of a capacitor by using a capacitor obtained by holding an insulated layer which has the insulated breakdown with the intermediate voltage between the 1st and 2nd power supply voltages between two electrode layers.

CONSTITUTION: An oxide film 7 is held between a polysilicone layer 6 and an aluminum layer 8 serving as two electrode layers to form capacitors C11, C12, C21 and C22. In a stand-by mode the potentials of all word lines are kept at Vcc with the potentials of all bit lines kept at 2Vth respectively. In a write mode the potential of only a selection word line WL2 is set at V22 and the potential of only a selection bit line BL1 is set at Vcc. As a result, diode D21 of a selection cell CL21 is biased adversely and the Vcc higher than the electrostatic voltage VBD is impressed to the capacitor C21. Thus the film 7 of the C21 is broken and the cell CL21 conducts.