The interface between the (001) surface of GaAs and a CoGa layer grown by molecular beam epitaxy has been characterized using transmission electron microscopy in plan view and cross‐sectional view. The interface is found to consist primarily of a network of edge dislocations with Burgers vectorsa[100] anda[010] (abeing the lattice parameter of the CoGa). The occurrence of these Burgers vectors indicates that these misfit dislocations are nucleated in the CoGa during growth. It is clearly shown that the threading dislocations in the CoGa originate at the misfit dislocations at the interface, while the GaAs layer underneath is free of dislocation.