Process for the production of semiconductor devices comprising the steps of applying a solution of the specified polycarbosilane in a solvent onto a substrate having electrically conductive components fabricated therein, and curing the coated layer of the polycarbosilane at a temperature of not less than 350.degree. C. in an oxidizing atmosphere to thereby covert the polycarbosilane layer to a silicon oxide layer. The resulting silicon oxide layer has a planarized surface and has no cracking and accordingly is useful as a dielectric layer and a protective layer in the production of semiconductor devices having a high reliability.