TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The lattice constant of the half-Heusler compound (main phase) is 0.5933-0.5947 nm or 0.6110-0.6130 nm (inclusive). In the thermoelectric material, a ratio of the maximum peak intensity (Ifull(220)x 100/Ihalf(220)) is less than 18%, preferably less than 6%, where Ihalf(220) is the maximum peak intensity in X-ray diffraction of the half-Heusler phase, and Ifull(220) is the maximum peak intensity in X-ray diffraction of the full-Heusler phase. In the thermoelectric material, a dimensionless figure of merit ZT (Z = S2 sigma /K, where S, sigma and K are Seebeck coefficient, electric conductivity and thermal conductivity, respectively and T is absolute temperature) is at least 0.05 at room temperature. Preferred Method: The cooling rate in the rapid cooling step is at least 100 degrees C/second. The method further comprises a sintering step in which powder obtained in the rapid cooling step is sintered. Preferred Definitions:    y = 0.015-0.145;    A1 = Y;    B1 = Co or Cu;    C1 = Al, Si or Sb;    y1 = 0.01-0.1;    A2 = Y, Sc, Nb, V, Ta or rare earth elements;    B2 = Cu, Ag, Au, Pd or Pt; and    C2 =Al, Si or Sb.    EXAMPLE - Titanium (Ti), nickel (Ni) and tin (Sn) were weighed so that their feed values could produce Ti(1- alpha )Ni(1- alpha )Sn ( alpha = -0.05 to 0.05) or TiNi(1+ beta )Sn ( beta = -0.01 to 0.03). These were placed into a crucible made of boron nitride and then placed in a high frequency induction furnace. After evacuating the inside of the furnace to 10-3 Pa, argon gas was introduced until the internal pressure within the chamber was raised to 0.34x 105 Pa. Subsequently, high frequency current was applied to a coil so that the raw material in the crucible was melted. Then the resultant molten metal was furnace cooled to obtain an ingot. The resultant ingot was remelted within a pipe made of boron nitride and then the molten metal was rapidly cooled on a copper roll surface rotating at 3000 rpm to obtain a ribbon shaped thermoelectric material, which was ground and then sintered under a pressure of 50 MPa at 1100 degrees Cx 15 minutes by using a spark plasma sintering apparatus.