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Advancing thermoelectric n-type Mg 3 Sb 2 alloys requires both high carrier concentration offered by effective doping and high carrier mobility enabled by large grains. Existing research usually involves chalcogen doping on the anion sites, and the resultant carrier concentration reaches ≈3 × 10 19 cm -3 or below. This is much lower than the optimum theoretically predicted, which suggets that further improvements will be possible once a highly efficient dopant is found. Yttrium, a trivalent dopant, is shown to enable carrier concentrations up to and above ≈1 × 10 20 cm -3 when it is doped on the cation site. Such carrier concentration allows for in-depth understand of the electronic transport properties over a broad range of carrier concentrations, based on a single parabolic band approximation. As well as reasonably high carrier mobility in coarse-grain materials sintered by hot deforming and fusing of large pieces of ingots synthesized by melting, higher thermoelectric performance than earlier experimentally reported for n-type Mg 3 Sb 2 is found. In particular, the thermoelectric figure of merit, zT, is even higher than that of any known n-type thermoelectric, including Bi 2 Te 3 alloys, within 300-500 K. This might pave the way for Mg 3 Sb 2 alloys to become a realistic material for n-type thermoelectrics for sustainable applications., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)