MBE InASySb1-y layers were grown at 370°C across the full composition range. TEM/TED examinations directly showed that separation into two phases had taken place for compositions 0.4<y<0.8 with plates 20 to 200nm thick occurring approximately parallel to the layer surface. The two phases in the individual specimens were tetragonally distorted and their compositions were deduced from the TED results. CuPt-type atomic ordering occurred and was most pronounced in the middle of the composition range. Alloy clustering was also present. Hall measurements showed that the carrier concentration was a maximum, and the mobility was a minimum, for the middle of the composition range.