Temperature-dependent chemical interactions between Au and nine III-V compound semiconductors (III = Al,Ga,In and V = P,As,Sb) have been calculated using bulk thermodynamic properties. Enthalpic considerations alone are insufficient to predict metal/ compound semiconductor reactivities. The entropy of vaporization of the group V elements is shown to be an extremely important driving force for chemical reactions involving the III-V's, since it enables several endothermic reactions to occur spontaneously under certain temperature and pressure conditions. Plots of either Gibbs' free energies of reaction or equilibrium vapor pressure of the group V element versus temperature are used to predict critical reaction temperatures for each of the systems studied. These plots agree extremely well with previous experimental observations of thin film reactions of Au on GaAs.