We investigated Al-doped ZnO nanowire gas sensors with various Al-doping ratios (0-6%) on sapphire substrates prepared by step edge decoration using pulsed layer deposition. High quality ZnO nanowires exhibited a diameter of about 20 nm and a regular interval of about 80 nm on sapphire substrates. For the Al doping of 3%, we obtained the highest sensitivity of about 170 for the ethanol concentration of 200 ppm. The highest sensitivity was obtained by a reduction in the lowest resistivity resulting from the optimum Al doping of 3% although the highest resistivity of the Al-doped ZnO nanowires was reduced. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3236797] All rights reserved.