We report a detailed study of GaAs/A1GaiAs double-barrier quantum wells grown by molecular beam epitaxy. In these structures the GaAs layers were embraced by thin AlAs barriers and then by Al033Ga067As outer barriers. It is shown that the insertion of one or two monolayer AlAs barriers has spectacular effects in changing the confinement energies. Numerical calculations have been performed within the envelope function approximation including the exciton corrections. The observed emission peak energies in low temperature photoluminescence spectra are in good agreement with the calculation values.