Described herein is a technique capable of improving the uniformity of device characteristics. A method of manufacturing a semiconductor device may include: (a) accommodating in a process chamber a substrate having an organic film thereon; (b) supplying a metal-containing gas to the substrate; (c) supplying a first oxygen-containing gas and a dilute gas to the substrate, the dilute gas containing at least one of a second oxygen-containing gas and an inert gas; (d) performing a cycle a predetermined number of time, the cycle including (b) and (c), wherein a flow rate of the first oxygen-containing gas is equal to or greater than a flow rate of the dilute gas in one of the cycle performed the predetermined number of time.