To provide a method of forming an electrode or interconnection suitable for a semiconductor device which operates in a high-temperature environment, and to provide a semiconductor device having the electrode or interconnection.

An interlayer insulation film 12 is formed on a substrate plane 10a of a semiconductor substrate 10 in such a manner as to cover lower layer interconnections 11, and interconnection trenches 13 are formed in the interlayer insulation film 12. Then, a metal film 14 is so formed as to cover the surface of the interlayer insulation film 12, the internal walls of the interconnection trenches 13, and the lower layer interconnections 11 by sputtering, CVD, or the like. Thereafter, oxidizing treatment is performed using oxygen plasma to oxidize the metal film 14, turning it into a barrier layer 15. Thus, a barrier layer 15 which is chemically stable even in a high-temperature usage environment at a temperature exceeding 200C and effectively works as a barrier layer can be interposed between Cu interconnections 18 and the interlayer insulation film 12, and thereby diffusion of Cu, which is a material of the interconnections, into the interlayer insulation film 12 can be prevented.