NOVELTY - Producing polycrystalline silicon by the thermal decomposition of silane in a fluidized bed reactor having a reaction chamber (10), comprises introducing one or more feed gases into the reaction chamber with the gases comprising silane, where the reaction chamber has a cross-section through which feed gases pass, and the fluidized bed reactor produces at least 100 kg/hour of polycrystalline silicon per square meter of reaction chamber cross-section, and the overall concentration of silane in the feed gases fed into the reaction chamber is less than 15 vol.%.    USE - The process is useful for producing polycrystalline silicon by the thermal decomposition of silane in a fluidized bed reactor having a reaction chamber (claimed), where the polycrystalline silicon is useful in integrated circuits and photovoltaic (i.e. solar) cells.    ADVANTAGE - The process is capable of efficiently producing the polycrystalline silicon with high productivity and without degrading the reactor performance by reducing the deposition of silicon deposits on reactor walls.    DETAILED DESCRIPTION - Producing polycrystalline silicon by the thermal decomposition of silane in a fluidized bed reactor having a reaction chamber (10), comprises introducing one or more feed gases into the reaction chamber with the gases comprising silane, where the reaction chamber has a cross-section through which feed gases pass, and the fluidized bed reactor produces at least 100 kg/hours of polycrystalline silicon per square meter of reaction chamber cross-section, the overall concentration of silane in the feed gases fed into the reaction chamber is less than 15 vol.%, the pressure in the reaction chamber is at least 3 bar, and silane thermally decomposes in the reaction chamber to deposit an amount of silicon on the silicon particles.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a fluidized bed reactor.    Distributor (2)    Feed gas (5)    Second feed gas (7)    Reaction chamber (10)    Freeboard region. (11)