ABSTRACTFour layer HgCdTe/CdTe/GaAs/Si structures have been prepared by the sequential growth of (100) GaAs on (100) Si by MBE, (100) CdTe on GaAs/Si by congruent evaporation in UHV and (100) HgCdTe on CdTe/GaAs/Si by vapor transport. Infrared transmission, X-ray rocking curves, differential interference contrast microscopy and selected area electron channelling patterns characterize the structures.