The present invention provides a multilayer wiring technology by which high adhesiveness and high insulation reliability between wirings are obtained, while maintaining effective low capacitance between wirings. A semiconductor device is characterized in that a first insulating film is an insulating film formed of at least one layer which contains a siloxane structure containing silicon, oxygen and carbon; the siloxane structure in the inner part of the first insulating film contains a larger number of carbon atoms than the number of silicon atoms; and a modified layer which containing a smaller number of carbon atoms and a larger number of oxygen atoms per unit volume than the inner part of the first insulating film is formed on at least one of an interface between the first insulating film and the metal and an interface between the first insulating film and a second insulating film.