GaN single crystals were prepared in a sealed stainless-steel tube container at 650-840 degrees C for 6-300 h using Ga, NaN3, and Na as starting materials. A thin GaN layer covered Na-Ga melt surface at the initial stage of reaction between Ga in the Na-Ga melt and N-2 given by the thermal decomposition of NaN3 around 300 degrees C. In the next stage, pyramidal and prismatic GaN single crystals grew under the layer. Prismatic and platelet crystals also grew from the melt which wetted the tube wall. The reaction rate was enhanced by increasing temperature and by increasing Na content in the melt. The maximum size of pyramidal crystals was about 0.7 mm. The platelet crystals were 1-2 mm in one direction and < 0.05 mm thick. The platelet single crystals prepared at 650 degrees C exhibited the sharpest cathodoluminescence peak with the strongest intensity at 362 nm.