Thermoelectric technology, harvesting electric power directly from heat, is a promising environmentally-friendly means of energy savings and power generation. The thermoelectric efficiency is determined by the device dimensionless figure of merit ZTdev, and optimizing this efficiency requires maximizing ZT values over a broad temperature range. Herein, we report a record high ZTdev ∼1.34, with ZT ranging from 0.7 to 2.0 at 300-773K, realized in hole doped SnSe crystals. The exceptional performance arises from the ultra-high power factor, which comes from a high electrical conductivity and a strongly enhanced Seebeck coefficient enabled by the contribution of multiple electronic valence bands present in SnSe. SnSe is a robust thermoelectric candidate for energy conversion applications in the low and moderate temperature range.