In a method of forming an epitaxial layer, an etching gas may be decomposed to form decomposed etching gases. A source gas may be decomposed to form decomposed source gases. The decomposed source gases may be applied to a substrate to form the epitaxial layer on the substrate. A portion of the epitaxial layer on a specific region of the substrate may be etched using the decomposed etching gases. Before the etching gas is introduced into the reaction chamber, the etching gas may be previously decomposed. The decomposed etching gases may then be introduced into the reaction chamber to etch the epitaxial layer on the substrate. As a result, the epitaxial layer on the substrate may have a uniform distribution.