The proposed improvement comprises, in a single crystal growing apparatus by the Czochralski method for semiconductor silicon: (A) providing a heat-resistant and heat-insulating covering board (20) in direct contact with the upper ends of the heat-insulating members (7) surrounding the quartz glass-made crucible and having a circular center opening; and (B) providing a heat-resistant and heat-insulating cylindrical tube (22) having an outer diameter approximately equal to the diameter of the center opening in the covering board as the component (A) air-tightly jointed to the upwardly extending conduit (5) and extending downwardly from the joint of the top wall of the metal-made housing and the upwardly extending conduit penetrating through the center opening in the covering board as the component (A) in such a manner that the single crystal (9) under growing is coaxially surrounded thereby, the lower end thereof being at a height above and in the proximity of the surface of the melt in the crucible. The silicon single crystal grown in the inventive apparatus is advantageous in preventing occurrence of defects such as OISFs on the wafer taken therefrom after a thermal oxidation treatment.
