We demonstrate the application of ultramicrotome techniques for the preparation of thin semiconductor interfaces in cross-section, for analysis by electron beam techniques. This is of significance for semiconductor device technology, since a specific area on a particular device may be examined in cross-section. High-resolution transmission electron microscopy studies of twinned structures at the interface of a 1.2 μm metal-organic chemical vapour deposited HgCdTe epilayer on {100} GaAs are reported. {100} epitaxial growth starts to dominate about 40 nm from the interface, and continues to the top surface of the epilayer. Energy-dispersive X-ray analysis shows that the mercury concentration within the epilayer increases as the interface is approached. No evidence of diffusion into the GaAs substrate was obtained.