A method of forming an oxide layer. The method includes: forming a layer of reaction-inhibiting functional groups on a surface of a substrate; forming a layer of precursors of a metal or a semiconductor on the layer of the reaction-inhibiting functional groups; and oxidizing the precursors of the metal or the semiconductor in order to obtain a layer of a metal oxide or a semiconductor oxide. According to the method, an oxide layer having a high thickness uniformity may be formed and a semiconductor device having excellent electrical characteristics may be manufactured.