We report on structural investigations of the plastic strain relief in the highly mismatched InAs/GaAs(001) system grown in the layer-by-layer growth mode. The misfit dislocation generation mechanism is observed to be anisotropic in the two perpendicular ⟨110⟩ directions. We explain this result by the interplay between the chemically inequivalent dislocation types present in compound semiconductors and the applied growth condition. ©1998 American Institute of Physics.