There are provided a method of manufacturing a semiconductor device, a substrate processing apparatus, and a semiconductor device. The method allows rapid formation of a conductive film, which has a low concentration of impurities permeated from a source owing to its dense structure, and a low resistivity. The method is performed by simultaneously supplying two or more kinds of sources into a processing chamber to form a film on a substrate placed in the processing chamber. The method comprises: performing a first source supply process by supplying at least one kind of source into the processing chamber at a first supply flow rate; and performing a second source supply process by supplying the at least one kind of source into the processing chamber at a second supply flow rate different from the first supply flow rate.