A comparative study of the effect of pulsed γ-neutron irradiation on the photosensitivity spectra of Si p – n photodiodes with active layers based on self-assembled GeSi nanoisland arrays and Ge epitaxial layers is performed. The irradiation of photodiodes with GeSi nanoislands is found to not lead to photosensitivity degradation in the spectral region of interband optical absorption in nanoislands (wavelength range of 1.1–1.7 μm). At the same time, a steady decrease in the intrinsic photosensitivity of Si and the photosensitivity of photodiodes based on Ge epitaxial layers with an increase in irradiation dose is observed. This effect is attributed to the accumulation of radiation-induced defects in the Si matrix and deep in Ge epitaxial layers, respectively.