An insulating film configuring an uppermost layer of a gate insulating film of a memory cell comprises a silicon oxide film and is a layer to which a metal or metal oxide is added. A formation step of the insulating film comprises the steps of: forming the silicon oxide film; and adding the metal or the metal oxide in an atomic or molecular state by a sputtering process onto the silicon oxide film. Oxide of the metal has a higher dielectric constant than silicon oxide, and the metal oxide has a higher dielectric constant than silicon oxide. A High-K added layer is thus used as the insulating film configuring the gate insulating film of the memory cell, thereby a high saturation level of a threshold voltage can be maintained while a drive voltage (applied voltage for erase or write) is reduced, leading to improvement in reliability of the memory cell.