Abstract: Provided are a precursor supply unit, a substrate processing system, and a method of fabricating a semiconductor device using the same. The precursor supply unit may include an outer container, an inner container provided in the outer container and used to store a precursor source, a gas injection line having an injection port, which is provided below the inner container and in the outer container and is used to provide a carrier gas into the outer container, and a gas exhaust line having an exhaust port, which is provided below the inner container and in the outer container and is used to exhaust the carrier gas in the outer container and a precursor produced from the precursor source.