in a method and an appratus for a thin film growth on a semiconductor crystal substrate , impurities and contaminants absorbed on the inside wall of the reaction vessel are very harmful because these impurities and contaminants will deteriorate the quality of the thin film . a method and an apparatus by which the quantity of these impurities and contaminants absorbed on the inside wall of the reaction vessel can be restrained and removed easily are disclosed in this invention , wherein a semiconductor crystal substrate is mounted in the reaction vessel , and the wall of the reation vessel is cooled forcibly by a coolant while the substrate is under heating procedure to grow a thin film on the substrate by supplying the raw material gas into the reaction vessel . and the temperature of the wall of the reaction vessel during the procedure except the thin film growth is kept higher temperature than the temprature of the wall of the reaction vessel during the thin film growth procedure .