Si doped amorphous silica films were prepared by rf magnetron sputtering technique. As-deposited films which had relatively low Si dopant were annealed in inert atmosphere, and spectroscopic analyses were performed for as-deposited and all the annealed samples by infrared (IR) absorption, X-ray fluorescence analysis, X-ray photoelectron spectroscopy (XPS) and Si-29 magic angle sample spinning nuclear magnetic resonance spectroscopy (Si-29 MAS-NMR). When the sample was annealed at 800 degrees C, the IR absorption peak located at 1080 cm(-1) shifted to slightly higher wave number. On the other hand, the decrease of Si clusters or Si-Si bonds in as-deposited film was deduced from X-ray fluorescence and XPS spectra for the sample annealed at 800 degrees C. These annealing characteristics of the films prepared in this study were discussed based on the random bonding model of SiOx film, and the spectral variations with thermal annealing were interpreted by the rearrangement of Si and O atoms in as-deposited films, rather than the simple clustering of excess Si atoms.