Hydrogen-enriched Si(100) and Si(lll) wafers were thermally oxidized and the growth kinetics were studied by measuring the thickness and the refractive index of the oxide. The oxidation was performed in dry oxygen at temperatures of 800, 845 and 855 degrees C. Prior to oxidation the Si surfaces were hydrogen-enriched by hydrogenation in hydrogen plasma in a planar r.f. unit. The substrates were kept at the lower electrode without heating or at a temperature of 100 degrees C. In the investigated thickness range of 40-200 Angstrom the growth was linear with time. The rate constant was smaller and the zero time thickness higher (as obtained from the fit of the experimental points) as compared with the case of the Si surface with wet RCA preoxidation clean only. A discussion on the role of the hydrogen in oxide growth mechanisms is included.