This work reports on the local structure and bonds of amorphous silicon oxynitride thin films, deposited by plasma enhanced chemical vapor deposition. The dependence of the structural properties and chemical bonds with the film’s composition was investigated. The used analytical techniques were X-ray absorption at the Si K-edge and Fourier transform infrared spectroscopies. The coordination numbers, interatomic distances and Debye-Waller disorder factors of the Si first shell and, the bond types and the concentration of hydrogen in the films were obtained. All the analyzed data support the formation of a material’s homogeneous network with a random distribution of Si-O and Si-N bonds. The basic structural element of the network is a tetrahedron with a central Si atom connected to N and O, consistent with a random bonding model. As the nitrogen content in the solid phase decreases the SiON3, SiO2N2 tetrahedral units gradually change to SiO4, keeping the quantity of SiO3N tetrahedrons almost unchanged, approximately 40%. The amount of SiO4 units is 100% for films with high oxygen content. The nitrogen is preferentially bonded to silicon and hydrogen, while the hydrogen is mostly bonded to nitrogen. © 2002 Elsevier Science Ltd. All rights reserved.