The invention provides a method of manufacturing semiconductor device by which a crystalline silicon film having excellent characteristics can be obtained by removing or reducing a metallic element existing in a crystalline silicon film obtained by utilizing the element and, at the same time, a highly efficient semiconductor device can be obtained by using the silicon film. In this method, the crystalline silicon film is obtained by crystallizing an amorphous silicon film through first heat-treatment after introducing the metallic element which promotes the crystallization of silicon into theamorphous silicon film. Then the semiconductor device is obtained by removing or reducing the metallic element existing in the silicon film and, at the same time, removing a formed thermally oxidizedfilm, by performing second heat-treatment in an oxidizing atmosphere and forming a thermally oxidized film on the surface of the area from which the thermally-oxidized film is removed by again performing thermal oxidation. In this method, an oxygen-containing oxidizing atmosphere, halogen-containing oxidizing atmosphere, or the like, is used as the oxidizing atmosphere.