The present invention provides a method for producing a half Heuslar alloy including quench-solidifying a molten alloy at a cooling rate of 1×102 to 1×103° C./sec to produce a Heuslar alloy represented by the formula: ABC (wherein A and B each is at least one member selected from transition metals such as Fe, Co, Ni, Ti, V, Cr, Zr, Hf, Nb, Mo, Ta and W, and C is at least one member selected from Group 13 or 14 element such as Al, Ga, In, Si, Ge and Sn), and a high-performance thermoelectric power generating device using the thermoelectric semiconductor alloy.