A plurality of memory cell transistors each of which has a gate structure having a floating gate electrode formed of a first conductive film and stacked on an element region surrounded by an element isolation region on a silicon substrate with a first insulating film disposed therebetween and a control gate electrode formed of a second conductive film and stacked on the first conductive film with a second insulating film with a large dielectric constant disposed therebetween are arranged in a memory cell array. A detrap pulse supply circuit generates and supplies a detrap pulse signal to the control gate electrode of the memory cell transistor to extract charges from the second insulating film after data is written into each of the memory cell transistors.