A method of manufacturing a semiconductor device, the method comprising: forming an oxide film on a substrate by alternately repeating: (a) forming an element-containing layer on the substrate by supplying a source gas containing an element into a process vessel accommodating the substrate; and (b) changing the element-containing layer to an oxide layer by supplying an oxygen-containing gas and a hydrogen-containing gas into the process vessel having an inside pressure lower than atmospheric pressure, reacting the oxygen-containing gas with the hydrogen-containing gas to generate oxidizing species containing oxygen, and oxidizing the element-containing layer by the oxidizing species; wherein the hydrogen-containing gas is supplied into the process vessel together with the source gas in step (a).