The transport properties of InP and GaAs epitaxial layers grown on exactly (001)‐oriented Si substrates were investigated by temperature‐dependent van der Pauw measurements combined with anodic stripping. Electron concentrationsnatT=300 K decreasing from around 1018cm−3at the heterointerface to a constant level of 1016cm−3toward the surface agree well with the concentration profile of Si donors. Their activation energy is 2.9 and 1.3 meV in InP/Si and GaAs/Si, respectively. At low temperatures a marked decrease of the electron mobility &mgr; at the heterointerface occurred. A quantitative analysis of &mgr; (T) led to the model of charged dislocations as scattering centers. By comparison with the dislocation densities of 2×108and 1×108cm−2in the vicinity of the surface of 2‐ and 3‐&mgr;m‐thick layers found by wet chemical etching we derived the occupation probability of the charged centers along the dislocation lines as 0.2 and 1.0 for InP and GaAs, respectively. At 300 K &mgr; was almost unaffected by dislocation scattering and values of 3600 cm2/(V s) (InP) and 3800 cm2/(V s) (GaAs) fornof 2×1016and 8×1016cm−3were obtained which are close to the values found with homoepitaxial layers. ©1995 American Institute of Physics.