A semiconductor device capable of high speed operation with a substantially small interlayer capacitance is produced by steps of using an insulating film comprising an organic insulating film and an insulating film composed of an organometallic polymer material as an interlayer insulating film formed by coating, patterning the insulating film in a semi-thermosetting state, etching the organic insulating film as the lower layer by means of the organometallic polymer as a mask, using a plasma gas containing oxygen as the main component, and then conducting ultimate baking treatment of these insulating films.