Heterostructures with biaxially compressed InAsSb are being considered as active regions for midwave infrared diode lasers. Quantum wells of biaxially compressed InAs1−xSbx(x≊0.09) in unstrained InAs were characterized using magnetophotoluminescence. The quantum size shift of the photoluminescence for a series of quantum wells produced an estimate of the conduction band offset. In magnetic field studies, the holes in the strained quantum wells exhibited a decrease in effective mass, approaching that of the electrons. A type I band offset was observed for these InAsSb/InAs heterostructures. Throughout this study, magnetoexcitonic behavior is observed; our analysis indicates that the exciton binding energy increases with quantum confinement. ©1995 American Institute of Physics.