Half-Heusler (HH) alloys (MgAgSb structure) are benchmark thermoelectric (TE) materials in the intermediate temperature range (400-800oC). These alloys exhibit good thermal stability, scalability, and high power density. For many years, the figure of merit (ZT) of HH alloys has stayed near 1. Despite the moderate ZT, a conversion efficiency near 9% was achieved in p-n couple modules. Recently, ZT as high as 1.3-1.5 have been reported. We herein report a systematic study on the role of V, Nb, and Ta as prospective resonant dopants in enhancing the ZT of n-type (Hf,Zr)NiSn half-Heusler alloys. The V doping was found to increase the thermopower in the temperature range 300-1000 K. In contrast, Nb and Ta act as normal dopants, as evident by the decrease in electrical resistivity and thermopower. The combination of enhanced thermopower due to V resonant states and the reduced thermal conductivity has led to ZT=1.3 near 850 K.