In this work, we report studies on the residual stress and structure of silicon oxynitride films deposited by PECVD with nitrogen atomic percent varying from 24 to 55. The stress response to thermal annealing at different temperatures is analyzed and correlated with Rutherford backscattering spectroscopy, ellipsometry, Fourier transform infrared spectroscopy, small-angle X-ray scattering spectroscopy and X-ray near edge absorption spectroscopy at the Si-K edge measurements. The results show that the stress varies from compressive to tensile for the as-deposited samples. The annealing process increased the stress value in samples that had a tensile behavior as-deposited, while decreased its value in samples with compressive stress as-grown. It is observed that the stress shifts with annealing in a way that can be correlated with the volume density of voids, also depending on the composition and structure of the films. © 2006 Elsevier B.V. All rights reserved.