PURPOSE: To make the surface of an electrode rugged so as to enlarge a charge storage region in area by a method wherein an insulating film which is possessed of defects and lacking in acid resistance is formed on the charge storage electrode material of a semiconductor memory device and then oxidized.

CONSTITUTION: Ions are implanted into a single-crystal or polycrystalline silicon 4 to turn its surface amorphous, and a silicon nitride film 7 is deposited thereon as thick as 4nm through a CVD method. The single-crystal or polycrystalline silicon 4 is thermally treated in a non-oxidizing atmosphere to be recrystallized, whereby a stress is applied to the silicon nitride film 7 to produce defects in it. The silicon 4 is subjected to a thermal treatment in an oxidizing atmosphere to oxidizing the silicon nitride film 8. In result, a silicon oxide film 9 which varies locally in thickness is formed, and an interface between the film 9 and the silicon 4 is repeatedly bent into folds. The silicon oxide film 9 is selectively removed. Therefore, the surface of a single-crystal or polycrystalline silicon is smoothly rugged, and a charge storage electrode surface 10 is increased in area and consequently enhanced in charge storing capacity. A capacity insulating film is improved in reliability.