The bismuth-tellurium alloy system was investigated by electromotive force measurements, coulometric titrations, x-ray diffraction, and differential thermal analyses. The thermodynamic properties of the system have been obtained from the electromotive force measurements. The partial molar free energy, enthalpy, and entropy have been measured as a function of alloy composition at 655°, 700°, and 766°K. The integral thermodynamic properties were computed from the experimental data. The heat of formation of the compound Bi2Te3 is estimated at −46 ±10 kcal/g mole at 766°K. The phase equilibrium diagram was established from experimental data. The results confirm that a very narrow single γ-phase region exists near the compound Bi2Te3.