Interfacial Si suboxides (SiOx, x<2) are detrimental to transistor performance and are typically minimized during postoxidation anneals. To study the kinetics of SiOx decomposition, thick films (similar to 2000 Angstrom) of amorphous Si:O:H alloys (0.7500 degrees C initially there is a rapid segregation into amorphous Si (a-Si) surrounded by a SiO2 shell which acts, as a diffusion barrier decelerating the reaction. Phenomenological modeling of kinetics with a one-dimensional Avrami-Erofe＇ve treatment gives an upper limit for a-Si lateral,growth rates of 1.2 Angstrom/s at 900 degrees C with an activation energy of 120 kJ/mol. FL, Raman, transmission electron microscopy and ellipsometry confirm this segregation model in the amorphous state. Due to the rapid initial decomposition and relatively large diffusion coefficients, a simple kinetic hindrance explanation for the 4-8 Angstrom of SiOx at the SiO2/Si interface is unlikely.