Recent studies suggest that the radiative conversion efficiency of mid-infrared semiconductor devices is limited by non-radiative Auger mechanisms. Band structure engineering techniques, such as the introduction of strain or the use of type-II band offset materials, have been shown to reduce the effect of Auger recombination. Results from light emitting diodes (LEDs) with an active region consisting of ten InAs/GaInSb/InAs/AlGaAsSb type-II ‘W’ quantum wells grown by molecular beam epitaxy (MBE) on GaSb substrates are described. At room temperature, the device was characterised by a slope efficiency of 98 µW/A at low currents, which dropped at higher currents due to heating. This corresponded to an internal efficiency of approximately 2.6%.