the invention relates to a semiconductor device having improved wiring layers . the wiring is formed on the semiconductor substrate and has a first region and a second region . the first region comprises a conductive film and an insulating film formed by oxidizing a film connected to the conductive film and made of the same material thereof . the second region includes a wiring and is provided on the first region . the gibbs free energy of the wiring decreases less than that of the conductive film when the wiring and the conductive film are oxidized .