Abstract: An apparatus for manufacturing a semiconductor device includes a boat configured to support a plurality of stacked substrates, a first tube surrounding the boat in a lateral direction and having a cylindrical shape with an upper portion thereof being open, and a cleaning gas supply nozzle extending from an outer portion of the first tube to a portion between an interior sidewall of the first tube and the boat. The cleaning gas supply nozzle may include a first segment extending from the outer portion of the first tube to an inner portion of the first tube, a second segment extending in a lengthwise direction of the first tube from an end of the first segment, and a third segment extending in a direction differing from the extension direction of the second segment from an end of the second segment.