In this article, we report on a systematic study of mid-IR, W-Integrated Absorber (W-IA), lasers that employ strained InAs/InxGa1−xSb/InAs active layers, in which the indium content of the hole bearing InxGa1−xSb has been varied from xIn=0 to xIn=0.45. The output characteristics of the lasers improve as the In percentage is increased; the threshold temperature sensitivity (T0) values are observed to increase from ≈35 to ≈50 K. Further, the differential quantum efficiencies as a function of temperature are significantly improved in the devices with xIn⩾0.25. For samples with nominally eight monolayers (8 ML) InAs/7 ML InxGa1−xSb/8 ML InAs, the lasing wavelength at 84 K is observed to shift from 3.33 μm for xIn=0 out to a maximum of 4.62 μm for xIn=0.35. This large shift is well predicted by an empirical psuedopotential model; the model also predicts that the position of the hole wave function is sensitively dependent on strain level and that for xIn<0.25, the holes are no longer confined in the W active region, but rather in the thick IA layers where they experience a bulklike density of states. This suggests that the improved thermal performance with increasing strain is due to the onset of hole quantum confinement in the W region, and improved or deeper hole confinement in that epitaxial layer. © 2002 American Institute of Physics.