Embodiments of the inventive concepts provide a method of cleaning a furnace-type semiconductor apparatus that is equipped in a clean room and includes a process chamber in which a process of forming a thin film is performed on a substrate. The method includes supplying air of the clean room into the process chamber after the process of forming the thin film, and thermally treating an inside of the process chamber using the air of the clean room supplied to the inside of the process chamber. An adhered material containing chlorine is formed on an inner surface of the process chamber by the process of forming the thin film, and the chlorine of the adhered material is removed by the thermal treatment of the inside of the process chamber.