In order to block hydrogen ions produced when forming an interlayer insulating film by HDP-CVD or the like to thereby suppress an adverse effect of the hydrogen ions on a device, in a semiconductor device including a contact layer, a metal interconnection and an interlayer insulating film on a semiconductor substrate having a gate electrode formed thereon, the interlayer insulating film is formed on the metal interconnection by bias-applied plasma CVD using source gas containing hydrogen atoms, and a silicon oxynitride film is provided in the underlayer of the metal interconnection and the interlayer insulating film.