It is an object of the present invention to provide, with good yields, a composition for forming an insulation film which allows obtaining an insulation film for a semiconductor device having a low dielectric constant, excellent stress resistance and excellent crack resistance; an insulation film for a semiconductor device formed from the composition for forming an insulation film; and a high quality and highly reliable semiconductor device fabricated using the insulation film for a semiconductor device. This composition for forming an insulation film comprises a polymer of which the main chain is a chain portion which substantially contains only carbon, silicon and hydrogen, and which contains nitrogen in portions other than the main chain. It is preferable that nitrogen exists as a constituent represented by Formula 1 in the polymer. ##STR00001##