A study has been made of the effect of dislocation density on the properties ofp‐type GaAs (Ge‐doped,p= 1 × 1019cm−3) grown homoepitaxially on GaAs and heteroepitaxially on GaP. It has been found that dislocation densities > 5 × 106cm−2reduce the minority‐carrier diffusion length in thep‐type material and, consistent with this reduction, degrade the junction electroluminescence andp‐layer photoluminescence. At high dislocation densities (> 5 × 106cm−2), it is also found that subgrains form in the GaAs epitaxial layers grown either heteroepitaxially on GaP or homoepitaxially on GaAs. It is surmised that the dislocations polygonize during growth to form subgrain boundaries rather than form due to nucleation at the substrate. Finally, the results indicate that the electron diffusion length is limited to the average dislocation spacing with the dislocations acting as nonradiative recombination centers for electrons.