Modulation-doped quantum wells (QWs) of GaSb clad by AlAsSb were grown by molecular beam epitaxy on InP substrates. By virtue of quantum confinement and compressive strain of the GaSb, the heavy- and light-hole valence bands in the well are split and the hole mobility is thereby significantly enhanced. Room-temperature Hall mobilities as high as 1200-1500 cm(2)/V s were achieved for 5-10 nm QWs and biaxial strains of 1-3%. This contrasts with earlier work on GaSb/AlGaAsSb QWs on GaAs substrates in which the mobilities were found to fall off above 1% strain. Moreover, unlike in comparable InGaSb and InSb QWs, the high mobilities were maintained out to sheet densities of 3.5 x 10(12)/cm(2). As a result, the sheet resistivities observed in the GaSb/AlAsSb wells reached record levels as low as 1500 Omega/square. Modeling indicates that this performance gain is due to the larger valence band offset of the GaSb QWs and the consequent reduction in scattering because of the better confinement and the lower doping levels needed for a given sheet charge. Published by Elsevier Ltd.