Photoresist removal method using hydrogen radicals, which are produced on a tungsten hot-wire catalyst, is effective to resolve some environmental and industrial problems in conventional methods for the fabrication of electronic devices. However, its removal rate is not as good as that of the conventional ones. We have previously described that the removal rate of a positive-tone novolac photoresist is enhanced by the addition of a small amount of oxygen gas to the atmosphere, in which hydrogen radicals are produced. Oxidizing radicals, such as OH and O radicals, can be produced together with H radicals. In present study, we examined the effects of oxygen addition on base polymers of KrF and ArF photoresists: the former is poly(vinyl phenol) (PVP), and the latter is poly(methyl methacrylate) (PMMA). Effects of oxygen addition on PVP was confirmed, as was found for the novolac photoresist. On the other hand, the effects on PMMA were different from the cases of the novolac photoresist and PVP. Results were ascribed to the presence or absence of benzene rings, the properties of polymers and the reactivity of oxidizing radicals.