Thin CdTe films have been grown epitaxially on GaAs(100) by molecular beam epitaxy. In the temperature range between 250 and 300°C, growth can occur in both the (100) and (111) epitaxial orientations. Using high-resolution transmission electron microscopy, we have studied the interface structure of these two cases. In parallel epitaxy, CdTe(100)/GaAs(100), the interface is atomically abrupt and slightly undulated. The 14.6% mismatch is relieved by the presence of a two-dimensional dislocation network at the interface. The dislocations run along 〈110〉 directions along the interface, with a periodicity of 31 Å, and have Burger's vector of 21a0〈100〉. In the case of CdTe(111)/GaAs(100), the interface is atomically abrupt with steps at the interface and CdTe(112) parallel to GaAs(110). Along these directions the atomic interplanar spacings match to within 0.7%. Pits in the GaAs substrate are evident with different densities in both cases, and are believed to be associated with the substrate surface treatment. © 1986.