ZnO nanowire-based CO gas sensors were fabricated by growing single crystal ZnO nanowires on patterned ZnO: Ga/ SiO2/ Si templates at various temperatures. It was found that the average length of the nanowires increased while the average diameter of the nanowires decreased as we increased the growth temperature from 600 to 700 degrees C. It was also found that the nanowires became significantly shorter as the growth temperature was increased. By measuring the resistivity change of the samples at 320 degrees C, it was found that the sensor responses were of 3, 17, 57, 7.5, and 5% for the ZnO nanowires grown at 600, 650, 700, 750, and 800 degrees C, respectively. Furthermore, it was found that the sensitivity of the sensor was relatively increased when the concentration of injected CO gas increased. (c) 2007 The Electrochemical Society.