InAsSb is a promising material for high operating temperature MWIR detectors. InAsSb p-n junction detectors dark current is g-r limited in the lower temperature range and diffusion limited in the higher ones. In this work we have investigated the properties GaSb / InAs0.91Sb0.09 heterostructure and its performance as a sensitive MWIR photodetector. The heterostructure was obtained by MOCVD growth of lattice matched, unintentionally doped layer of InAsSb on N-GaSb substrate. This rectifying N-n heterostructure has the unique type II broken gap interface. I-V and spectral response were measured at various temperatures in the range 20-300 K. The BLIP temperature was found to be 180 K. R0A product of 2.5 and 180 Ω·cm 2 were measured at 300 and 180 K, respectively. Dual color detection was demonstrated. The range of spectral response, due to light absorption in GaSb or in InAsSb can be determined by the applied bias. An optical gain larger than one was observed at temperatures below 120 K. High detectivity values of 1.3·1010 and 4.9·109 cm·Hz 1/2 W-1 at 180 and 300 K respectively were measured.