(GaIn)(NAs)/GaAs multi-quantum-well heterostructures are grown by metal organic vapor phase epitaxy at low temperatures and are subsequently annealed in the reactor to optimize optoelectronic properties. Detailed optical and structural studies of the properties of the material, which change upon annealing under different As-stabilization as well as at different temperatures, reveal that there are two major effects of the anneal. The first one is the blue-shift of the fundamental band gap of the material, which can be attributed to a local change in the group-III environment of the nitrogen atoms. The second observation is a strong increase in photoluminescence (PL) intensity and decrease in PL linewidth upon anneal in H-2-ambient, which can be attributed to the removal of non-radiative defects in the material. Chain-like N-ordering in growth direction, which induces strong inhomogeneous strain fields in the material and which can be dissolved upon anneal in H-2-ambient might also act as one of the main non-radiative recombination centers in the (GaIn)(NAs) material system. (c) 2006 Elsevier B.V. All rights reserved.