A method of manufacturing a semiconductor device is disclosed. The method includes forming a film on a substrate by performing a cycle a predetermined number of times, wherein the cycle includes non-simultaneously performing: supplying a precursor gas to the substrate in a process chamber; exhausting the precursor gas in the process chamber through an exhaust system; confining a reaction gas, which differs in chemical structure from the precursor gas, in the process chamber by supplying the reaction gas to the substrate in the process chamber while the exhaust system is closed; and exhausting the reaction gas in the process chamber through the exhaust system while the exhaust system is opened.