We have investigated by high-resolution X-ray diffraction, secondary-ion-mass-spectroscopy (SIMS) and Raman scattering the effects of rapid thermal annealing on the structural properties of GaNxAs1-x ternary alloys coherently grown on GaAs (001) substrates by molecular beam epitaxy. X-ray diffraction indicates that the in-plane strain does not relax and the vertical lattice in the GaNAs film tends to shrink, while SIMS reveals the absence of any N concentration change upon annealing. Furthermore, post-growth annealing causes an increase of substitutional N as revealed by the increase of the ratio of Raman scattering intensity between the nitrogen-localized vibration mode and the GaAs-like LO. After performing strain analysis, we conclude with the changes of N configurations in the GaNxAs1-x from the N-N split interstitial to the N-As split interstitial and the N-As substitutional at elevated temperatures, the thermal behaviors of N-N. N-As and N-As are reported over 700-850 degrees C. (c) 2006 Elsevier B.V. All rights reserved.