Zinc oxide (ZnO) films have been prepared by thermal oxidation of vacuum deposited zinc (Zn) films onto glass substrate kept at room temperature (35 degrees C). The structural, electrical, optical and gas sensing properties of films annealed at 350 and 500 degrees C have been investigated. X-ray diffraction measurements indicate that the ZnO films oxidized at these temperatures are polycrystalline in nature with (101) as preferential crystallographic orientation. Practically no change in lattice parameters of ZnO films is observed when oxidation temperature is increased from 350 to 500 degrees C. Field emission scanning electron microscopy shows nanoparticles and nanowires at the surface of the ZnO films oxidized at 350 and 500 degrees C, respectively. At room temperature (35 degrees C), the film oxidized at 350 degrees C shows a gradual increase of response up to 96% for 2000 ppm exposure of ethanol, while film oxidized at 500 degrees C could detect a response of 99% for 500 ppm beyond which it saturates. An increase in the optical absorbance of the film has also been observed when ethanol concentration increases from 50 to 200 ppm beyond which no significant change is noticed even up to 2000 ppm. (C) 2010 Elsevier B.V. All rights reserved.