Amorphous silicon thin films were deposited by dc reactive magnetron sputtering and posthydrogenated in order to investigate the H diffusion kinetics in a network originally free of H. A flux of atomic H was generated by dissociation of molecular hydrogen on a hot filament. Secondary ion mass spectroscopy was used to characterize the H profiles at various stages of diffusion. H profiles measured from secondary ion mass spectroscopy can be fitted by a complementary error function. The H diffusion exhibits a dispersive behavior, and the diffusivity in the a-Si is about I X 10(-15) cm2 s-1 at 340-degrees-C and t = 240 min. The dispersive parameter alpha was estimated to be approximately 0.4. The activation energy was approximately 0.4 eV. In order to improve the sensitivity at low concentration, posthydrogenation was also done with deuterium. Secondary ion mass spectroscopy analysis shows that at high D concentration the profile follows a complementary error function behavior, while at low concentration D profile follows an exponential decay. These results show that the posthydrogenation in dc magnetron sputtered amorphous silicon can be described by the combined effects of deep and shallow traps.