Thermal annealing improves the radiative efficiency of dilute nitride GaInNAs alloys, but the band gap of the GaInNAs alloys is found to blueshift. The structural changes of these alloys would occur during thermal annealing. In this study, we studied the local atomic configuration around In atoms using fluorescence extended X-ray absorption fine structure (EXAFS) spectroscopy and investigated the experimental results by computational calculations. From the EXAFS results for a pair of GaInNAs thin films, it was found that the number of In atoms surrounding N atoms increases after thermal annealing. Computational calculations based on a density functional theory were carried out. The distances from the In atom to the second-neighbor group Ill atoms were derived, and the values were consistent with the EXAFS results. © 2005 Elsevier B.V. All rights reserved.