High-quality InAs0.8Sb0.2 lattice matched to AlSb has been successfully grown on semi-insulating InP substrates by gas source molecular beam epitaxy using an AlSb/AlAs0.5Sb0.5 buffer layer structure. Due to the inserted AlAs0.5Sb0.5 layer between AlSb and InP, a two-dimensional growth mode is always maintained during the growth. Despite the large lattice mismatch between the InAs0.8Sb0.2 epilayer and InP substrate, the room temperature electron mobility of a 2000 A thick InAs0.8Sb0.2 has reached similar to 15 000 cm(2)/V s. Compared with InAs0.8Sb0.2 grown on GaAs using a single AlSb buffer layer, this method requires a thinner (<= 1 mu m) buffer layer structure. (C) 2008 American Vacuum Society.