A charge trapping layer in an element isolation region and that in an isolation region between a memory transistor and a selection transistor are removed so that the charges are not injected or trapped in the regions. Also, in an element isolation region, gate electrodes of each memory transistor are united at a position higher than a gate electrode of the selection transistor from a surface of a silicon substrate in an element isolation region, thereby reducing the capacitance between the memory transistor and the selection transistor.