Poly-Si is a widely used material for thermoelectric devices due to its CMOS compatibility. However, most of the studies focus on room temperature properties of this material. In this paper the authors present experimental results for a temperature range of -50oC to 300oC in which thermoelectric properties of heavily doped n/p-type poly-Si are measured and investigated, including electric resistivity, thermal conductivity and Seebeck coefficient. The experimental results shows that the figure of merit of the heavily doped poly-Si increases continuously, indicating better thermoelectric efficiency of the heavily doped poly-Si with higher temperature.