A method of achieving ultrahigh power factor and output power density in half-Heuslers containing Niobium (Nb), Titanium (Ti), Iron (Fe) and Antimony (Sb). Sintering the compounds from nano powders and levitating the sintering temperature up to 1373 K we found that grain size is drastically larger, resulting in higher carrier mobility and ultimately higher electrical conductivity and much higher power factor. The highest power factor of ~106 μW cm-1 K-2 has been achieved in Nb0.95Ti0.05FeSb. The high power factor resulted in an record output power density of ~22 W cm-2 measured with the cold side and hot side temperatures of 293 K and 868 K, respectively. Such a high output power density is beneficial for large-scale thermoelectric power generation applications.