Zinc oxide crystals were grown using hydrothermal method, and the habit faces were indexed by computing from inter-axial angles of the as grown boules. The dislocation structures were studied using synchrotron white beam X-ray topography. Grown-in dislocations as well as process-induced defects were characterized in the ZnO crystals. Knoop and Vickers micro-hardness were studied on sliced crystal plates. Chemical etching was used to study the dislocations running perpendicular to the wafer. (c) 2006 Elsevier B.V. All rights reserved.