Isothermal sections in the Ga-N-Na ternary phase diagram were calculated to provide a greater understanding of GaN crystal growth process with Na as the flux. The calculations were performed by combining the three binary systems. Thermodynamic modeling of the Ga-Na system was carried out based on existing experimental phase diagram and thermodynamic data. Self-consistent thermodynamic parameters for the Ga-Na system were obtained. Thermodynamic data and phase boundaries of the Ga-N binary system were taken from the literature. The N-Na system was estimated as an ideal solution in this study. The calculated sections reveal that the phase regions involving GaN and the liquids with a composition range of Na at 0.38-0.75 might be favored to GaN crystal growth. These predictions are consistent with an analysis of the experimental work of GaN crystal growth using the sodium flux method. (C) 2007 Elsevier B.V. All rights reserved.