When an oxidation treatment for regenerating a gate insulating film 6 is performed after forming gate electrodes 7A of a polymetal structure in which a WNx film and a W film are stacked on a polysilicon film, a wafer 1 is heated and cooled under conditions for reducing a W oxide 27 on the sidewall of each gate electrode 7A. As a result, the amount of the W oxide 27 to be deposited on the surface of the wafer 1 is reduced.