The role of hydrogen peroxide in RCA standard clean was roughly clarified by angle-resolved photoelectron spectroscopy and infrared absorption spectroscopy such that the oxidation by basic hydrogen peroxide results in a negligible amount of Si-H bonds in native oxide, while the oxidation by acidic hydrogen peroxide results in a small amount of Si-H bonds in native oxide. It is also found that oxidation in a boiling solution of HNO3 results in large amount of Si-H bonds in native oxide as in the case of oxidation in a hot solution of HNO3.