We present a study of ballistic-electron-emission microscopy (BEEM) and spectroscopy on epitaxial CoSi2(100)/Si(100) interfaces. The Schottky barrier height deduced from these measurements is surprisingly nonuniform. In particular, at dislocations with Burgers vectors (b) over right arrow = a/4[111] and at other as yet unidentified defects, the barrier is reduced to near zero. The disturbing influence of BEEM contrast due to varying surface reconstructions could be minimised by modifying the surface with a thin Fe silicide, leading to uniform root 2 X root 2 R 45 degrees reconstruction. In this way, the spatial extent of the barrier variation was found to be as small as 4 nm.