The present invention discloses the new thermoelectricmaterials, i.e., Mg3Bi2-based Zintl phase compounds. We discovered that the semi-metallicMg3.2Bi2 (nominal composition) shows an unexpectedly large Seebeck coefficient of -107 μV K-1at 350 K and very promising thermoelectric performance. Such a high Seebeck coefficient shouldbe attributed to the very large electron-to-hole weighted mobility ratio above 8. By partialsubstitution of Bi with Sb, the thermoelectric performance of Mg3.2Bi2-based materials can besubstantially improved. The optimized Mg3.2Bi1.498Sb0.5Te0.002 shows a peak ZT of ~0.9 at 350 K.The n-type Mg3.2Bi2-based materials are highly promising for thermoelectric cooling application.A unicouple of n-type Mg3.2Bi1.498Sb0.5Te0.002 and p-type Bi0.5Sb1.5Te3 was prepared and a largetemperature difference of ~91 K can be realized with the hot-side temperature of ~350 K.