PURPOSE: To suppress crystal defects in a semiconductor substrate by a method wherein a supporting unit which is extended vertically and plate-shaped supporters which are continuous with the supporting unit and extended horizontally and which have widths smaller than the diameters of the semiconductor substrates which are subjected to a heat treatment and the semiconductor substrates are put on the top surfaces of the supporters.

CONSTITUTION: A heat treatment boat has a supporting unit 11 which is extended vertically and plate-shaped supporters 12 which are continuous with the supporting unit 11 and extended horizontally and which have widths smaller than the diameters of semiconductor substrates which are subjected to a heat treatment. The heat treatment boat is loaded with the semiconductor substrates 4 in such a manner that the center part of each substrate 4 is placed on the top surface of the supporter 12 which is a placing surface 13 with its main surface 4a on which semiconductor chips are formed facing upward. Then, the semiconductor substrate 4 is warped only upward convexly. Further, when the semiconductor substrate 4 is taken out from an electric furnace after the heat treatment, the direction of the transient deformation of the semiconductor substrate 4 is the same as the direction of the warpage in the electric furnace. Therefore, crystal defects in the semiconductor substrate 4 can be suppressed.