The knowledge of diffusion processes in semiconducting alloys is very important both technologically and from a theoretical point of view. Here we show that, self-diffusion in Si1−xGex alloys as a function of temperature and Ge concentration can be described by the cBΩ thermodynamic model. This model connects the activation Gibbs free energy of point defects formation and migration with the elastic and expansion properties of the bulk material. The approach allows the systematic investigation of point defect thermodynamic parameters such as activation enthalpy, activation entropy and activation volume, based on the thermo-elastic properties (bulk modulus and its derivatives, mean atomic volume and thermal expansion coefficient) of the two end-members of the Si1−xGex alloy. Considerable deviations from Vegard’s law are observed, due to the diversification of the bulk properties of Si and Ge, in complete agreement with the available experimental data.