This invention provides a process for producing an organic polymer film whereby when using it as an interlayer insulating film in a semiconductor device, the film exhibits higher adhesiveness at its interfaces where other semiconductor materials are in contact with the lower and the upper surface of the film while an effective dielectric constant in the whole organic polymer film can be further reduced. Specifically, a plurality of organic monomers vaporized is sprayed onto a heated substrate surface via plasma generated in a reaction chamber to form a copolymer film comprising frame composed of a plurality of organic monomer units. During the process, relative ratio between the feeding rate of the organic monomer molecules is varied along the progress of the film growth to continuously grow an interlayer insulating film in which films having good mechanical strength and adhesiveness with rich content of siloxane-structure are set near the interfaces (91a,c, 92a,c or 93a,c) and a film having a lower bulk density are arranged as an intermediate layer (91b, 92b or 93b) sandwiched therebetween.