To inhibit increase in film thickness calculated in terms of the film thickness of a silicon oxide film as the whole gate insulating film and to constitute an ultrathin gate insulating film containing an insulating film having a high dielectric constant as its main component.

In a method of manufacturing a gate insulating film 20, which is interposed between a semiconductor substrate 4 and a gate electrode 22, nitrogen 12-containing ions are implanted in a region, which is formed with the gate insulating film, on the substrate 4 and an insulating film 18 consisting of a high-dielectric constant material is formed within the region implanted with ions to contrive to manufacture the film 20. Thereby, an ultrathin gate insulating film containing the film 18, which inhibits increase in film thickness calculated in terms of the film thickness of a silicon oxide film and has a high dielectric constant, as its main component can be constituted.