A semiconductor wafer serving as a treatment target has a stack structure in which a high-dielectric-constant gate insulating film is formed on a silicon base material with an interface layer film of silicon dioxide sandwiched therebetween, and a metal gate electrode containing fluorine is further formed thereon. A heat treatment apparatus radiates flash light from a flash lamp to the semiconductor wafer in an atmosphere containing hydrogen to carry out heating treatment for an extremely short period of time of 100 milliseconds or less. As a result, diffusion of nitrogen contained in the metal gate electrode is inhibited, at the same time, only the fluorine is diffused from the high-dielectric-constant gate insulating film to an interface between the interface layer film and the silicon base material to reduce an interface state, and reliability of the gate stack structure can be improved.