Thin films of undoped and chromium (Cr)-doped zinc oxide (ZnO) were synthesized by RF reactive cosputtering for oxygen gas sensing applications. The prepared films showed a highly c-axis oriented phase with a dominant (0 0 2) peak appeared at a Bragg angle of around 34.13 degrees, which was lower than that of the standard reference of ZnO powder (34.42 degrees). The peak shifted to a slightly higher angle with Cr doping. The operating temperature of the ZnO gas sensor was around 350 degrees C, which shifted to around 250 degrees C with Cr-doping. The response of the sensor to oxygen gas was enhanced by doping ZnO with 1 at.% Cr. Impedance spectroscopy analysis showed that the resistance due to grain boundaries significantly contributed to the characteristics of the gas sensor. (C) 2011 Elsevier B.V. All rights reserved.