Described herein is a technique capable of forming a sacrificial film with a high wet etching rate so as to obtain a wet etching selectivity with respect to a movable electrode when manufacturing a cantilever structure sensor. According to one aspect of the technique of the present disclosure, there is provided a method of manufacturing a semiconductor device including: (a) placing a substrate with a sacrificial film containing impurities on a substrate support in a process chamber, wherein the sacrificial film is formed so as to cover a control electrode, a pedestal and a counter electrode formed on the substrate; (b) heating the substrate; and (c) modifying the sacrificial film into a modified sacrificial film by supplying an oxygen-containing gas in a plasma state to the substrate to desorb the impurities from the sacrificial film after (b).