GaN buffer and main layers were grown by the conventional hydride vapor phase epitaxy technique using GaCl3 consecutively. The deposited buffer layers were investigated by, atomic force microscopy and X-ray analysis. To examine the behavior of the buffer layers at main layer growth temperature, heat treatment was conducted at 900degreesC. Based on the results of the buffer layer study, GaN thick films were grown at 1050degreesC. Optimum deposition conditions of buffer layer from the buffer and main layer studies generally coincided. On the phi scanning pattern, the GaN films grown on (0001) Al2O3 were single-crystalline. Band-edge emission dominated photoluminescence was observed at room temperature.