High-quality and low cost bulk crystals are needed in the field of group III nitride semiconductors in order to develop optical and electrical devices. There are two approaches for the growth of bulk GaN crystal by the Na flux method. One is to grow thick GaN crystal on a large seed GaN crystal grown by vapor phase method. The other is to grow GaN crystal on a small seed GaN crystal. 3 in diameter GaN crystals were grown on the large GaN seed crystal. In the case of the growth on a small GaN seed, we obtained bulk crystal with a pyramidal shape and its height and diameter were 15 mm and > 20 mm, respectively. We also present the effects of the impurity in the solution on the property and growth habit. (C) 2011 Elsevier B.V. All rights reserved.