There is provided a process for forming a silicon oxide film which is useful as an electrical insulating film, dielectric film or protective film as used in LSI, thin-film transistor, photoelectric converter, photosensitive body and the like. The process comprises forming a coating film from a polysilane compound represented by the formula SinRm (wherein n is an integer of 3 or more, m is an integer of n to 2n+2, and a plurality of R's are independently a hydrogen atom or an alkyl group) and oxidizing the coating film to form the silicon oxide film.