Using an optical fiber thermometer, wafer temperature was measured during implantation at elevated temperatures. The wafer was mounted on a chuck which was resistively heated to 400 °C. Ar was implanted at an energy of 200 keV and a current in the range of 0–750 μA. Due to poor thermal contact between the chuck and the wafer, wafer temperature could be different from chuck temperature. The wafer temperature varied from ∼300 to 500 °C as a function of implantation current. The wafer temperature was also dependent on the optical properties of the wafer. A model was developed which took the optical properties of the wafer and the chuck into account.