Abstract: Native ZnO films were fabricated by pulsed laser deposition with two different kinds of ZnO powder (99.5% and 99.99%). Atomic force microscopy was used to investigate the film morphology and toughness, and X-ray diffractmetry for characterizing the crystal structures. The results indicated that the two samples had similar morphologies and the same crystal structure. By Hall effect measurements it was found that the two samples exhibited electrical properties of low resistivity and high Hall mobility but of opposite conduction type. Further analyses indicated that the Si substrates played a key role in the measurements of the electrical properties for both samples. A secondary ion mass spectrum measurement of the lower purity ZnO/Si sample showed that S diffused into the Si substrate near the interface, which led to the inversion of the substrate conduction type.