Hydrogenated amorphous silicon was grown from disilane by rf glow discharge. Deuterium (D) was used as a tracer gas in this investigation, in which two gas mixtures (Si2H6+D2and Si2D6+H2) were employed. Amorphous silicon so produced was analyzed for1H and D by Rutherford recoil measurement to determine whether these elements came from disilane or dilution gas. When the rf power is low, a much larger proportion of hydrogen atoms in disilane (1H in case of Si2H6, D in case of Si2D6) than in the dilution gas is found in the amorphous silicon. The exact reverse is true as the rf power becomes large.