Tin monoxide, SnO, is known as a p-type semiconductor. Comparison of the energy levels with the band alignment of oxide semiconductors implies that SnO is bipolar, and carrier polarity conversion to n-type was achieved by Sb doping. The electron mobility and the donor level are similar to 2 cm(2) (V s)(-1) and similar to 90 meV, which are similar to the hole mobility and the acceptor level in p-type SnO. n-Type conduction was further confirmed by the rectification characteristics of a homo p/n junction. A concept for realizing bipolar oxide semiconductors with high visible transparency is proposed. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3505288] All rights reserved.