A method of manufacturing a semiconductor device may include forming a material layer on a substrate, performing a selective oxidation process to form a capping oxide layer on a first surface of the material layer, wherein a second surface of the material layer is not oxidized, and etching the material layer through the second surface to form a material pattern. An etch rate of the capping oxide layer is less than an etch rate of the material layer. A semiconductor device may include a lower electrode on a substrate, a data storage part on a top surface of the lower electrode, an upper electrode on the data storage part, and a capping oxide layer arranged on at least a portion of a top surface of the upper electrode. The capping oxide layer may include an oxide formed by oxidation of an upper surface of the upper electrode.