In combination with scanning electron microscopy and x‐ray pole‐figure analysis high resolution electron microscope (HREM) observation of the diamond‐silicon cross section in a ⟨001⟩ epitaxially oriented diamond film was carried out to investigate the atomic interfacial microstructure. The films were prepared by microwave plasma chemical vapor deposition using a bias‐enhanced nucleation technique. Due to the multiple fit of diamond and silicon lattices, there is a periodic 3‐to‐2 registry of {111} atom planes of the epitaxial diamond‐silicon interface. Planar defects on diamond {111} planes and interface misfit dislocations are shown for epitaxially oriented and for slightly misoriented diamond crystallites. A cubic silicon carbide ‘‘transition’’ is found to be unnecessary for the epitaxy. The misorientation of the grown crystallites is also studied and found to be probably due to interface imperfection. ©1995 American Institute of Physics.