In a method of forming a thin layer for a semiconductor device through an ALD process and a CVD process in the same chamber, a semiconductor substrate is introduced into a processing chamber, and an interval between a showerhead and the substrate is adjusted to a first gap distance. A first layer is formed on the substrate at a first temperature through an ALD process. The interval between the showerhead and the substrate is additionally adjusted to a second gap distance, and a second layer is formed on the first layer at a second temperature through a CVD process. Accordingly, the thin layer has good current characteristics, and the manufacturing throughput of a semiconductor device is improved.