A technique of manufacturing a semiconductor device of stable operation is provided. There is provided a method of manufacturing a semiconductor device comprising a first process of forming an insulating film from a nitrogen-containing organic metal used as raw material, on a semiconductor layer by atomic layer deposition; a second process of processing the insulating film by oxygen plasma treatment in an atmosphere including at least one of oxygen and ozone; and a third process of processing the insulating film by heat treatment in a nitrogen-containing atmosphere, after the second process.