The applicability of the Lifshitz‐Slyozov model for predicting phosphorus precipitation rates in the phosphorus‐SiGe system is investigated. Model parameters are determined from short‐term anneals of less than 2000 h for SiGe alloys varying in silicon content from 67 to 81 at.% and prepared by zone leveling or hot pressing. Using these parameters in the model, resistivity changes are predicted for phosphorus‐doped SiGe thermoelectric elements which had been life tested from 4000 to 40 000 h. It is concluded that the Lifshitz‐Slyozov model is applicable to the phosphorus‐SiGe system. The results of this study can be used to calculate long‐term degradation of thermoelectric performance in SiGe alloys due to phosphorus precipitation.