Room-temperature Ti/Al ohmic contact on undoped AlGaN/GaN heterostructure was demonstrated through surface treatment using N-2 inductively coupled plasma. The specific contact resistivity was reduced from Schottky behavior to 1.02 x 10(-4) Omega cm(2) by the treatment. Increases in Ga-N binding energy and production of metallic Ga and Al conducting layers were found at the treated surface. This indicates that N vacancies, acting as donors for electrons, were produced at the treated surface, resulting in a shift of the Fermi level to near the conduction band, via the formation of ohmic contact. (C) 2002 The Electrochemical Society.