NOVELTY - A reactor (100) with source gas supply nozzles (9) is used for producing polycrystalline silicon (13). Precipitation reaction of polycrystalline silicon is performed at 0.25-0.9 MPa, when flow rate of source gas at gas supply port of source gas supply nozzle is u (m/second), source gas feed rate is Q (kg/second), and the internal volume of reactor is V (m3), the values of u and Q of source gas supply nozzle are set in such a way that sum total is 2500 (kg/m.second3) or more, to supply of source gas to reactor for producing polycrystalline silicon (13).    USE - Supply of source gas to reactor for producing polycrystalline silicon (claimed) used as raw material of single crystal silicon substrate for semiconductor device fabrication and solar cell manufacture.    ADVANTAGE - The method controls the rate of occurrence of popcorn by adjusting the kinetic energy of source gas supplied to reactor. The kinetic energy of source gas becomes a parameter at the time of scaling up reactor.    DETAILED DESCRIPTION - A reactor having one or more source gas supply nozzles from which the flow pattern of source gas in reactor becomes upward flow in reactor center portion, and becomes downflow in reactor outer-wall side portion is used for producing polycrystalline silicon. During precipitation reaction of polycrystalline silicon under the reaction pressure of 0.25-0.9 MPa, when the flow rate of the source gas at gas supply port of the source gas supply nozzle is u (m/second), source gas feed rate is Q (kg/second), and the internal volume of the reactor is V (m3), the each value of u and Q of the source gas supply nozzle are set in such a way that sum total (~S) (Qx u2/V) of value (Qx u2/V) is 2500 (kg/m.second3) or more, to supply of source gas to reactor for manufacturing polycrystalline silicon by Siemens method. An INDEPENDENT CLAIM is included for polycrystalline silicon, which is obtained by depositing the source gas by Siemens method.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional schematic view of reactor for polycrystalline silicon production.    Base plate (5)    Gas supply nozzle (9)    Electrode (10)    Polycrystalline silicon (13)    Reactor (100)