The equilibrium pressures of N-2 over Ga/GaN were measured from 1055 to 1350 K. We find that GaN is stable up to 1210 +/- 30K at 1bar N-2. We obtain values of -165 +/- 16 kJ/mol, -136 +/- 14J/molK, and 19 14 kJ/mol K for the standard enthalpy of formation, the standard entropy change of formation, and the absolute entropy, respectively. The minimum partial pressure of NH3 in H, for the stable growth of GaN was measured as a function of temperature and gas flow rate through the reactor. These data were used to define an upper bound on the standard Gibbs free energy. This upper bound is consistent with the results from the equilibrium N-2 pressure measurements. (C) 2008 Published by Elsevier B.V.