Abstract: Thermodynamic activities of gallium were measured between 1073 and 1273 K in the nonstoichiometric intermetallic compound Ni₃Ga using an emf-method based on solid oxygen-conducting electrolytes. The partial molar enthalpies and entropies were derived from their dependence on temperature. The results of the activity measurements were interpreted in terms of a statistical-thermodynamic model for nonstoichiometric phases with the cubic Ll₂-superstructure considering four types of point defects, i. e-antistructure atoms and vacancies on the nickel- and gallium-sublattice. The enerpies of formation of the point defects at the stoichiometric composition are used as adjustable parameter.