The authors report a two-color quantum well infrared photodetector at room temperature operating in the mid- and long-wavelength infrared detection. To this purpose, the band alignment is tailored and electronic properties are investigated for the proposed structure based on Ga1−xInxAsySb1−y/GaSb and AlxGa1−xAsySb1−y/GaSb. As accurate knowledge of band offsets is required in device modeling, we have proceeded to theoretical investigations of the band offsets for pseudo-morphically strained and lattice-matched Ga1−xInxAsySb1−y/GaSb and AlxGa1−xAsySb1−y/GaSb heterointerfaces in the whole range of alloy compositions 0 ≤ x, y ≤ 1. The carrier effective masses are deduced from the laws extracted from the k.p strain Hamiltonian laws. For the modeled heterostructure, the dark current of about 10−1 A cm−2 at ambient temperature shows the high performance of this multi-color infrared photodetector around 5 and 12.5 µm wavelengths.