Microstructural and electrical properties of potentiostatically electrodeposited ZnO thin films from an aqueous bath were investigated after annealing at different temperatures in Ar and 5% H-2/Ar atmospheres. It is confirmed that the bandgap energy of ZnO thin films decreased with annealing from 3.42 to 3.27-3.29 eV by calculating the wavelength of the absorption region. The annealing at temperatures as low as 200 degrees C decreased the sheet resistance of ZnO thin films because of the extinction of Zn(OH)(2) in the atmosphere. In addition, the sheet resistance of ZnO thin films decreased by annealing in a 5% H-2 atmosphere, which caused an increase of carrier concentration by hydrogen reduction. (C) 2011 Elsevier B.V. All rights reserved.