Provided is a technique capable of uniformizing the characteristics of a film after a plurality of substrates are processed. A method of manufacturing a semiconductor device may include: (a) loading a substrate into a process chamber; (b) processing the substrate by performing: (b-1) supplying and exhausting a process gas into and from the process chamber without activating the process gas; (b-2) supplying and exhausting the process gas into and from the process chamber while activating the process gas; (b-3) measuring an amount of impurity desorbed from the substrate while performing (b-2); and (b-4) measuring a gas exhausted from the process chamber after performing (b-3); (c) calculating a process data based on: a first measurement data obtained by repeating (b-3); and a second measurement data obtained by repeating (b-4); and (d) determining whether to terminate (b) based on the process data.