PURPOSE: To provide a MOS transistor, in which the film thickness of a gate oxide film can be thinned even when a polysilicon gate MOS transistor is not used.

CONSTITUTION: A silicon oxide film 9 is formed onto an N-type silicon wafer 3 as a gate oxide film. A CrSi thin-film 10 as a thin-film material having the standard generated free energy of an oxide larger than silicon is formed onto the silicon oxide film 9. A TiW thin-film 11 as a gate electrode is arranged onto the CrSi thin-film 10. An aluminum wiring 12 is used as a wiring material. A temperature is increased to a high temperature through aluminum sintering, but SiO2 has -178Kcal and Cr2O3 -148Kcal as the standard generated free energy of the oxide, and SiO2 is more stable than Cr2O3. Accordingly, the reaction of 2CrSi+3SiO2→Cr2O3+5Si is not generated, and the thickness of the gate oxide film is not changed.