A method of forming a film, which comprises the steps of coating a liquid raw material comprising a precursor of film-forming material dissolved in a solvent, on a surface of substrate, and forming a solid film on the surface of substrate by subjecting the substrate to a plurality of heat treatments differing in heating temperature from each other. The heat treatments differing heating temperatures from each other are performed over the same single hot plate. The film to be formed may be an organic SOG film. There is also disclosed a method of manufacturing a semiconductor device, which comprises the steps of coating a liquid raw material for forming an organosilicon oxide film on a surface of semiconductor substrate, and subjecting the semiconductor substrate to a first heat treatment where the semiconductor substrate is heated in an oxidizing atmosphere and at a temperature of 200° C. or more.