Negative differential resistance was observed in current-voltage curves of ZnO nanowire embedded sensors in the ethanol environment and conductances at critical points are inversely proportional to the concentration, while this phenomenon was not observed in the toluol environment. Through individual ZnO nanowire experiments, we attribute negative differential resistance to the joint effect of electron transference in the oxidation process of hydroxyls and the nonequilibrium occupation factor for electrons in the process saturating with generation rate of carriers at the ZnO nanowire surface. The inverse variation is associated with the densities of donor and acceptor traps. These results indicate that surface depletion can be beneficial to nanodevices. (C) 2011 Elsevier B.V. All rights reserved.