Enrichment of metallic single-wall carbon nanotubes (SWCNTs) up to 80 % has been achieved by preferable oxidation of semiconducting SWCNTs simply by keeping HiPco® SWCNTs in hydrogen peroxide at 90 ºC for 47 min. The higher chemical reactivity of semiconducting SWCNTs was probably caused by a metallization of semiconductors due to a charge transfer to the hydrogen peroxide. This reaction could be applied to more precise selection that is crucial to transparent electrodes and the other electronic devices in near future.