Abstract: Elemental silicon is produced by a process and apparatus wherein relatively impure silane (SiH.sub.4) is purified in the gaseous state, while mixed with an inert carrier gas, to a content of electronically active impurities which is no higher than that of "electronic grade" silicon. The silane so purified is then thermally decomposed to form elemental silicon of electronic grade purity, without need for further purification of the elemental silicon itself. The silane purification is carried out by injecting the impure silane gas as a series of timed, spaced pulses into a carrier gas stream which transports the silane pulses to a gas chromatographic column, through which the pulses flow in sequence. The column has a porous polymer or a molecular sieve packing which is specially preconditioned to achieve high resolution separation of the components of the feed.