Optical absorption measurements have been performed in InAs–GaSb superlattices to demonstrate the effect of spatial separation of carriers. From these and additional magneto-absorption measurements, the absorption edge is shown to arise from transition involving ground sub-bands of electrons and heavy holes. Fine structures in the spectra are identified with transitions from the excited sub-bands of both heavy and light holes to the sub-bands of electrons, which are governed by the spatial overlap of their associated wavefunctions.