R. F. power and d. c. bias were simultaneously applied to an electrode in a conventional plasma chemical vapor deposition (PCVD) system in order to suppress the reduction reaction of SnO2 induced by a hydrogen-containing plasma. It was found that the position of the positive column on the substrate was shifted to the rf electrode by increasing dc bias voltage. As a result, the reduction reaction of the SnO2 surface exposed to hydrogen plasma is dramatically suppressed.