PURPOSE: To prevent erroneous storage caused by α particles irradiated from a radioactive atom of infinitesimal amount contained in a package by forming a metallic film made of elements of 72∼79 of atomic numbers on the surface of a semiconductor substrate formed with memory cells.

CONSTITUTION: There are formed a number of memory cells 31, a peripheral circuit 32 for operating the memory cells 31, an insulating film 33 formed on the entire surface except the connecting portions of the respective elements, and a wiring metal 34 for electrically connecting between the respective elements on the main surface of a semiconductor substrate 30, and a protective film 35 made of silicon oxide, silicon nitride or the like on the surface to cover completely the circuit 32. Further, a metallic film 36 made of gold is so formed on the surface 35 as not to make contact with the metal 34 exposed by a photoetching process of the like. The film 36 may be formed of elements of 72∼79 of atomic numbers having large preventive capacity of α particles 37 in addition to the gold.