In this paper, we developed high-k Tb2O3 poly-Si thin-film transistors (TFTs) using different CF4 plasma power treatments. The high-k Tb2O3 poly-Si TFT device with a 20-W plasma power exhibited better electrical characteristics in terms of a highly effective carrier mobility, a high-driving current, a low-threshold voltage, a small subthreshold slope, and a high ION/IOFF current ratio. This result is attributed to the incorporation of fluorine atoms into the Tb2O3/poly-Si interface to reduce the trap-state density. The high-k Tb2O3 poly-Si TFT prepared under a 20-W CF4 plasma power also enhanced electrical reliabilities, including hot carrier and positive bias temperature instability. All of these results suggest that the CF4 plasma-treated poly-Si Tb2O3 TFT is a good candidate for high-performance low-temperature poly-Si TFTs.