The yttrium partial enthalpies of mixing (Delta(mix)(H) over bar (Y)) and the integral enthalpies of mixing (Delta(mix)H) of liquid Ga-Ge-Y alloys have been determined by high-temperature mixing calorimetry for five sections with constant ratios of Ga and Ge at 1760 K. Plots of concentration dependence of Delta(mix)(H) over bar (Y)/(1 -X-Y)(2) show sharp inflections, which correspond to transition of the liquid alloys into heterogeneous state and can be used for determination of liquidus surface. Furthermore, the Delta(mix)H has been estimated in the ternary system using seven geometric models and the Bonnier model has been chosen as the most adequate one. The differences between the experimental and model integral enthalpies of mixing have been described by polynomial concentration dependence. The possible contribution of binary and ternary intermetallide compounds into the thermodynamics of the liquid Ga-Ge-Y alloys has been considered. (C) 2005 Elsevier B.V. All rights reserved.