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Half-Heusler phases (space group <inline-formula> <math display="inline"> <semantics> <mrow> <mi mathvariant="normal">F</mi> <mover accent="true"> <mn>4</mn> <mo>&#175;</mo> </mover> <mn>3</mn> <mi mathvariant="normal">m</mi> </mrow> </semantics> </math> </inline-formula>, C1_b) have recently captured much attention as promising thermoelectric materials for heat-to-electric power conversion in the mid-to-high temperature range. The most studied ones are the RNiSn-type half-Heusler compounds, where R represents refractory metals Hf, Zr, and Ti. These compounds have shown a high-power factor and high-power density, as well as good material stability and scalability. Due to their high thermal conductivity, however, the dimensionless figure of merit (<i>zT</i>) of these materials has stagnated near 1 for a long time. Since 2013, the verifiable <i>zT</i> of half-Heusler compounds has risen from 1 to near 1.5 for both n- and p-type compounds in the temperature range of 500&#8315;900 &#176;C. In this brief review, we summarize recent advances as well as approaches in achieving the high <i>zT</i> reported. In particular, we discuss the less-exploited strain-relief effect and dopant resonant state effect studied by the author and his collaborators in more detail. Finally, we point out directions for further development.