A semiconductor device having an improved contact hole through an interlayer insulator. A first insulating film comprising silicon nitride is deposited. A second insulating film comprising silicon oxide is deposited on the first insulating film. The deposition condition of the second insulating film is varied during the deposition so that the etching rate of the second insulating film increases from a lower portion toward an upper portion. Thereby, a contact hole which is formed by etching through the first and second insulating films has a tapered configuration to improve a reliability of a connection made therein.