Abstract: There is provided a method of erasing a nonvolatile semiconductor storage having a floating gate electrode with a constant threshold voltage of a memory cell transistor after an erasing operation and further with high security of superior repeat characteristics of a writing and an erasing operation and voltages free of miss-writing. On the erasing operation, a p-type semiconductor substrate is made into an earth ground, a drain is made into a floating potential and continuous pulses of negative high voltage of which parameters of multiplying pulse intervals by applying pulse numbers is 0.1 seconds or more are applied to a control gate electrode to perform intermittently the Fowler-Nordheim tunnelling of electrons from a floating gate electrode to the p-type semiconductor substrate.

Abstract: A non-volatile memory includes a sheet-shaped source line consisting of a conductive layer. The source line includes an opening at an area including a bit contact area above a drain diffusion layer. The bit contact is formed through self-alignment to the opening of the source line and a control gate electrode. In such a structure, a pitch of the bit contact in the direction parallel to the control gate electrode can be set to be a value twice of the minimum size in design.