PURPOSE: To reduce the nonuniformity in characteristics of separate wafers and in one wafer, by narrowing the intervals of cuts for mounting wafers in the end portions of a boat for heat treatment of a semiconductor and by widening same in the central portion of the boat.

CONSTITUTION: A boat 1 for heat treatment of a semiconductor whereon wafers 2 are mounted at prescribed positions is inserted and set in a semiconductor heat treatment tube 4, a cap is put on, treatment gas is introduced, the temperature inside the treatment tube is adjusted to be a prescribed value, and then heat treatment is conducted. On said occasion, the intervals of wafers are narrowed in the end portions of the boat for heat treatment of a semiconductor in which a turbulent flow occurs, so as to restrict the amount of treatment gas connected on wafers, while the intervals of wafers are widened in the central portion of said boat in which a laminar flow occurs, so as to facilitate the adherence of treatment gas on wafers. Thereby the nonuniformity in characteristics of separate wafers and in one wafer is reduced.