Type-II GaAs/AlAs quantum-well samples grown by low-pressure metal-organic vapour-phase epitaxy consisting of 50 periods of either 2 monolayers (ML), 4 ML, 5 ML, 6 ML, or 7 ML GaAs embedded in 28 ML AlAs were under investigation. Even at room temperature dominant type-I luminescence has been observed. The peak wavelength of this emission ranges from 620 to 440 nm and is determined by the GaAs layer thickness. A comparison of the measured transition energies with model calculations applying an effective mass approach and an empirical tight-binding Green's function scheme confirmed this strong dependence. To our knowledge this is the first report on intense yellow, green, and blue luminescence from GaAs. 1998 Published by Elsevier Science B.V. All rights reserved.