A process for preparing polycrystalline silicon comprising the steps of (A) reacting trichlorosilane with hydrogen thereby forming silicon and an effluent mixture comprising tetrachlorosilane and disilane described by formula HnCl6—nSi2 where n is a value of 0 to 6 and (B) co-feeding the effluent mixture and hydrogen to a reactor at a temperature within a range of about 600 C. to 1200 C. thereby effecting hydrogenation of the tetrachlorosilane and conversion of the disilane to monosilanes.