The amount of oxygen vacancies on the surface of SnO2 nanowires was controlled by N-2 plasma. Nitrogen ions in N-2 plasma were substituted for oxygen vacancies (V-o) on the nanowire surface, reducing the amount of oxygen vacancies. Photoluminescence spectra showed that the V-o-related peak around 600 nm decreased dramatically after N-2 plasma and increased again after ultravioleto-zone (UVO) treatment. The threshold voltage (V-th) of the SnO2 nanowire transistors exhibited a +1.8 V positive shift after N-2 plasma, and the V-th of the N-2 plasma-treated nanowire transistors shifted toward the negative direction (-0.76 V) again after UVO. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3562274] All rights reserved.