Abstract: The method for manufacturing a silicon oxide film is characterized in that the method includes the steps of forming the silicon oxide film by a vapor deposition method or the like and of irradiating infrared light onto this silicon oxide film. Thus, according to the present invention, a silicon oxide film of relatively low quality formed at relatively low temperature can be improved to be a silicon oxide film of high quality. When the present invention is applied to a thin-film semiconductor device, a semiconductor device of high operational reliability and high performance can be manufactured.