Experimental measurements are reported of the effect of mechanical stress on minority‐carrier lifetime in germanium and silicon. Lifetime has been measured as a function of temperature and for stress in the ⟨111⟩, ⟨100⟩, and ⟨011⟩ directions at stress levels up to 1010dyn/cm2. The lifetime changes were found to be reversible, and changes in lifetime of as much as a factor of 3 were observed at stress levels of 1010dyn/cm2. For all samples investigated, lifetime was observed to increase inn‐type material and to decrease inp‐type material. A theoretical model has been developed for explaining the effects of mechanical stress on minority‐carrier lifetime in germanium and silicon. The model is an extension of the Shockley‐Read model to account for stress‐induced splitting of the conduction and valence bands plus a possible shift in energy of recombination levels with stress.