We present energy loss spectra of Si–Ge heterojunctions. The early stage of formation of the interface has been studied by successive evaporations of small amounts of germanium on a silicon substrate heated at 350 °C. The results, compared with theoretical calculations, show that the interface is abrupt on a microscope scale and that germanium induces extrinsic interface states in the main and partial gaps of the projected bulk band structure of silicon on the (111) surface.