Cadmium zinc telluride has been developed as a room temperature radiation detector in recent years. The issue of decreasing surface leakage current, which affects the energy resolution of radiation response, was investigated extensively by various surface oxidation treatments. In this study, an aqueous solution of hydrogen peroxide (H2O2) was used in the oxidation of CdZnTe wafers in order to decrease surface leakage current. The surface chemical composition and its morphology modification due to this oxidation process were investigated. X-ray photoelectron spectroscopy analysis revealed that the main chemical species left after H2O2 oxidation are TeO2 along with a small amount of a Cd-related oxide. We found no obvious evidence of the presence of Zn-related oxides. The oxide thickness reaches a saturation after 5 min of H2O2 oxidation. The atomic force microscopy images revealed that, at this stage of saturation, the surface roughness and the mean diameter of the main features were about 1.3 μm and 97 nm, respectively. The decrease of 37% in the surface leakage current was related to the oxide layers formed by H2O2 oxidation.