PURPOSE: To make connecting holes without excessive etching process by a method wherein a flat surfaced etching mask is applied to an insulating layer on a substrate for making openings; the openings are filled up with a material whose volume is to be reduced by setting; and after the setting process, the setting material and the insulating layer are successively removed.

CONSTITUTION: A resist mask 5 with openings 6, 7 is provided on an Si substrate 1 covered with a PSG layer 4 having wirings 2, 3 and diffused layers 8. When a spin on glass layer 9 is applied to the whole surface and dried up, the volume of the layer 9 is reduced to 30% turning into a coated layer 19. When plasma-etched using CHF3, the layers 10, 4 both comprising SiO2 are etched away at the same rate. The time required for the complete connection equals the sum of the film thickness of both layers 10 and 4. In such a constitution, the difference in the thickness of the PSG layer 4 can be decreased by the spin on glass layer 10 so that the excessive etching of the substrate 1 may be reduced.