A semiconductor device having a barrier insulating film covering a copper wiring is formed by a plasma enhanced CVD method. The method includes supplying high frequency power of a frequency of 1 MHz or more to a first electrode, and holding a substrate on which copper wiring is formed on a second electrode facing the first electrode; supplying a film forming gas containing an alkyl compound and an oxygen-containing gas between the first and second electrodes while regulating gas pressure of the film forming gas to 1 Torr or less; and supplying high frequency power to either of the first and second electrodes to convert the film forming gas into a plasma, and allowing the alkyl compound and the oxygen-containing gas of the film forming gas to react to form a barrier insulating film covering the surface of the substrate.