We have realized a (GaAs1−xSbx‐InyGa 1−yAs)/GaAs bilayer‐quantum well (BQW), which consists of two adjacent pseudomorphic layers of GaAs1−xSbxand InyGa1−yAs sandwiched between GaAs barriers. Photoluminescence was observed at longer wavelengths than those found for corresponding InyGa1−yAs/GaAs and GaAs1−xSbx/GaAs single quantum wells (SQW), which indicates a type‐II band alignment in the BQW. The longest 300 K emission wavelength achieved so far was 1.332 &mgr;m. For an accurate determination of the band offset between GaAs1−xSbxand GaAs, required for a theoretical modeling of the interband transition energies of these BQWs, a large set of GaAs1−xSbx/GaAs SQWs was prepared from which a type‐II band alignment was deduced, with the valence band discontinuity ratioQvfound to depend on the Sb concentrationx(Qv=1.76+1.34x). With this parameter it was possible to calculate the expected interband transition energies in a BQW structure without any adjustable parameters. The calculations are in agreement with experimental data within a range of ±4%. ©1995 American Institute of Physics.