In this work an optically integrated and compact point temperature sensor based upon upconversion fluorescence emission in an Er3+-doped silica-on-silicon waveguide is proposed. The sensing system relies upon the temperature information residing in the intensity ratio of two thermally coupled upconversion excited fluorescence emission signals around 530 and 550 nm due to the Er3+ transitions 2H11/2→4I15/2 and 4S3/2→4I15/2, respectively. The system was tested in the range of temperature from 20 °C to 140 °C. Under this circumstance the system have shown sensitivity close to 9.0×10-3/°C with a coupled pump power around 800 nm as low as 7 mW and a maximum sensitivity of 0.010/°C is expected at 250 °C. © 2002 American Institute of Physics.