A material layer, a semiconductor device including the material layer, and methods of forming the material layer and the semiconductor device are provided herein. A method of forming a SiOCN material layer may include supplying a silicon source onto a substrate, supplying a carbon source onto the substrate, supplying an oxygen source onto the substrate, supplying a nitrogen source onto the substrate, and supplying hydrogen onto the substrate. When a material layer is formed according to a method of the present inventive concepts, a material layer having a high tolerance to wet etching and/or good electric characteristics may be formed, and may even be formed when the method is performed at a low temperature.