A method of forming a semiconductor device includes: loading a wafer onto a susceptor, wherein the susceptor is disposed inside a chamber; heating the inside of the chamber; and rotating the susceptor, and first forming a film on the wafer by outputting a reactive gas and a carrier gas from an injector disposed at a sidewall of the chamber to form a semiconductor device having a first layer, wherein the first layer is manufactured under a first condition, wherein the injector includes a first outlet exposed within the chamber to discharge the carrier gas directly into the chamber and a second outlet exposed within the chamber to discharge the reactive gas directly into the chamber, wherein the first outlet is disposed below the second outlet.