Abstract: A method for curing spin-on-glass formed on a wafer film which insulates the metal layers and flattens any step difference in the process for manufacturing a multi-layered metal layer of a highly integrated semiconductor device which comprises establishing a predetermined initial temperature in a heating chamber with an ultraviolet light source. A wafer, on which a SOG film to be cured is formed, is then introdued into the heated chamber and the temperature gradually increased to a predetermined maximum temperature. The SOG film is irradiated with ultraviolet light at a predetermined wavelength simultaneously with the application of heat at the maximum temperature for a predetermined time. The wafer is then cooled.