There is formed on a semiconductor substrate a lamination of a first insulating film of nondoped silicon glass or the like and, on this first insulating film, a second insulating film of boron phosphor silicate glass or the like, with a conductor layer between the two insulating films. A hole is first dry-etched in the second insulating film, leaving the substrate surface covered by the first insulating film. Then the second insulating film is heated to a reflow temperature such that the hole is thermally deformed, flaring as it extends away from the insulating film. Then a second hole is dry-etched in the first insulating film through the first recited hole in the second insulating film, with the consequent exposure of the semiconductor surface. Then a contract electrode is fabricated by filling the first and the second hole with an electroconductive material into direct contact with the substrate surface. Being covered by the first insulating film, the substrate surface is not to be contaminated with impurities during the heating of the second insulating film.