To provide a heat insulation heat insulating tool for a semiconductor wafer heat treatment furnace which eliminates the need of vacuuming the inside of a cylinder of a heat insulation heat insulating tool, is high in safety and excellent in productivity, workability, and treatment properties, and is capable of securing the smooth flow of processing gas, and demonstrating a sufficient heat insulation heat insulating effect.

The heat insulation heat insulating tool for the semiconductor wafer heat treatment furnace serves to place thereon a wafer support boat in the heat treatment furnace equipped with a disk-shaped silica glass bottom plate, a silica glass cylinder erected on the upper surface side of the bottom plate, and a silica glass top plate for closing the upper part of the cylinder. In the tool, there is provided heat shielding silica glass for partitioning the inside of the silica glass cylinder at least into an upper space and a lower space, and there is drilled a glass vent hole in hollow part wall surface of the silica glass cylinder.