To provide a semiconductor manufacturing device, which is provided with a wafer holder capable of improving the cooling rate of a heater and retaining the homogeneity of the temperature distribution of the heater at cooling time and which can markedly shorten the time period for treating a semiconductor wafer.The wafer holder includes the heater 1 for carrying the semiconductor wafer thereon to heat the same, and the cooling block 2 for cooling the heater 1. The cooling block 2 is arranged so as to come into and out of abutment against the back 1b of the heater on the side opposed to the wafer carrying face 1a, and its abutment face 2a to abut against the heater 1 has a warpage of 1 mm or less. The cooling block 2 can be provided therein with a passage for a cooling liquid. It is preferred that the passage has a sectional area of 1 mm2 or larger over 80% of its entire length, and that the area of the portion having the passage formed is 3% or larger of the entire area of the abutment face 2a.