Abstract The paper is devoted to the relationship between the energy gap and the saturation currents (diffusion and recombination ones) of GaInAs homo p–n junctions. Such a relationship is required for developing multi-junction solar cells and photodetectors for a given wavelength. The saturation currents and the energy gap have been determined experimentally, and an empirical exponential formula was obtained for the required relationship. The results of the work allow predicting the saturation current for a GaInAs p-n junction with a given energy gap.