The hydrothermal method combined with a platinum inner container was applied to grow zinc oxide (ZnO) single crystals. High-purity and transparent single crystals with a large -size of 50 x 50 x 15 mm 3 were successfully grown. The higher crystallinity of the hydrothermally grown ZnO crystal compared with the commercial ZnO substrate grown by the chemical vapor transport method was confirmed by X-ray diffraction. The + c region of the crystal is colorless and the -c region of it is pale green, relating to the unique residual impurity distribution. In the photoluminescence spectrum, a strong emission from the band edge at 3.3 eV was observed. On the other hand, the emission from the deep level at 2.2 eV was not observed. These results clearly indicate that this study assures the commercialization of the 2-in-size ZnO single crystal for future wide band gap device applications. (C) 2003 Elsevier B.V. All rights reserved.