We have grown heterostructures based on low band-gap channels of Ga xIn 2−xSb ( x=0.5) and InAs xSb 1−x ( x=0.4−1) alloys, and characterized be closely lattice them using Hall measurements. For barrier layers, we used Al xIn 1−xSb( x=1−0.5), with a composition chosen to matched to the channel layers, Ga x In 1- x Sb and InAs xSb 1−x. We also grew a Al xGa 1−xAs /GaAs ySb 1−y/GaAs pseudomorphic heterostructure, which is an analog of the In xGa 1−xAs pseudomorphic MODFET. In the case of Al xIn 1−xSb/ Ga xIn 1−xSb and Al xIn 1−xSb/InAs xSb 1−x heterostructures, the barrier layers were undoped but we observed two-dimensional electron densities of about 7×10 11 to 2×10 12 cm −2 at 300 K. For the AlSb/InAs and Al 0.7In 0.3Sb/Ga 0.7In 0.3Sb heterostructures, the 300 K mobilities were 24,000 and 3000 cm 2/V⋯s, respectively. Mobilities for the Al xIn 1−xSb/InAs xSb 1−x heterostructures were around 12,000 cm 2/V⋯s. Hall measurements on the Al xGa 1−xAs/GaAs ySb 1−y/GaAs heterostructures indicated 2D electron densities of 3×10 12 cm −2 and mobilities of 3,000 cm 2/V⋯s. These results indicate the potential of the Al xIn 1−xSb/InAs xSb 1−x ( x=0.4) heterostructures to be used as high-speed MODFETs and of the Al xGa 1−xAs/GaAs ySb 1−y/GaAs heterostructures to be used as power MODFETs.