Defect chemistry plays an important role in the p-type conductivity of transparent CuAlO2 thin films. Presence of excess oxygen atoms within the crystallites sites or interstitial sites is responsible for the enhanced hole-conductivity of p-CuAlO2+x thin films. These excess oxygen atoms within the films were induced by post-deposition annealing of the films in oxygen atmosphere. Composition analyses of the films confirmed the presence of nonstoichiometric (excess) oxygen within the films. With increase in the post-deposition annealing time, more and more oxygen atoms were intercalated within the p-CuAlO2+x thin films. Electrical conductivity measurements of the films indicated that with increase in the excess oxygen contents within the films, the p-type conductivity also increased. This observation supports the origin of p-type conduction in CuAlO2+x thin films due to excess oxygen atoms. (C) 2005 Elsevier B.V. All rights reserved.