GaSb-based heterostructures with strained-layer GaSb/Ga 1−x In x Sb(x = 0.26 or x = 0.35) single quantum wells and Al 0.5 Ga 0.5 Sb cladding layers were grown by molecular beam epitaxy. The thickness of the GaInSb well was varied from 3.0 to 14.5 nm. Intense room-temperature electroluminescence was observed from mesa diodes with peak emission wavelengths in the 1.9-2.2 µm spectral range. The dependence of emission energy on well thickness is consistent with the predictions obtained by an effective mass treatment assuming a rectangular type I quantum well and a conduction band offset E c = 0.6 E g .