A heater has a smooth heating surface and a recess formed on a second surface opposite to the heating surface. The recess is formed between opposite side walls in a lengthwise direction of the heater. Formation of the recess improves the electrical resistance of the heater and the opposite side walls reinforce the heater and prevent deformation of the heater when it is subjected to high temperatures in a semiconductor wafer processing device. The heater has substantially the same width along its lengthwise direction. This improves the control of heat pattern design, because the terminal end portions do not have an expanded shape.