Described herein is a technique capable of improving a controllability of a thickness distribution of an oxide film formed on a surface of a substrate. According to one aspect of the technique, there is provided a method of manufacturing a semiconductor device, including: (a) forming a first oxide layer by supplying an oxygen-containing gas and an hydrogen-containing gas to a heated substrate at a first pressure less than an atmospheric pressure and by oxidizing a surface of the substrate; and (b) forming a second oxide layer by supplying the oxygen-containing gas and the hydrogen-containing gas to the heated substrate at a second pressure less than the atmospheric pressure and different from the first pressure and by oxidizing the surface of the substrate on which the first oxide layer is formed.