Self-assembled ZnO 3D nanostructures were fabricated on a Si substrate using a simple hydrothermal process with ammonia and zinc acetate clihydrate solutions at 95 degrees C. The changes in morphology and characteristics of the ZnO nanostructures were investigated over a range of pH (9.0-11.8). The texture of the ZnO crystal was evaluated using the texture coefficient (TC) for the specific reflecting plane. The results showed that pH is the main factor affecting the morphology of the ZnO nanostructure. The ZnO nanostructures fabricated were single-crystalline with good crystal quality. The PL spectra showed that the ZnO nanostructures fabricated at pH >10.0 had good optical properties with low defect content. This demonstrates that the morphology of ZnO nanostructures fabricated using a simple hydrothermal process can be controlled by the pH of the solution. (C) 2008 Elsevier B.V. All rights reserved.