A method of manufacturing a semiconductor device, includes: forming a thin film containing silicon, oxygen and carbon or a thin film containing silicon, oxygen, carbon and nitrogen on a substrate by performing a cycle a predetermined number of times. The cycle includes supplying a precursor gas serving as a silicon source and a carbon source or a precursor gas serving as a silicon source but no carbon source, and a first catalyst gas to the substrate; supplying an oxidizing gas and a second catalyst gas to the substrate; and supplying a modifying gas containing at least one selected from the group consisting of carbon and nitrogen to the substrate.