In this paper, electrical characteristics by various oxygen content in ZnO films were studied. To control the oxygen content of ZnO films, post-thermal annealing was performed in N-2 and air ambient, led to improve crystallinity and optical properties of ZnO films. The oxygen concentration was measured by Auger electron spectroscopy. The ZnO films having the deficiency of oxygen showed the electron concentrations between 10(21) and mid 6 x 10(17) cm(-3) and resistivity at 10(-3)-10(-1) Omega cm. On the other hand, when the oxygen concentration of the ZnO films was up to the stoichiometry with Zn, the ZnO films showed low electron concentration at -10(17) cm(-3) and resistivity at 10 Omega cm. (c) 2007 Elsevier Ltd and Techna Group S.r.l. All rights reserved.