Thermal management of Integration Circuit (IC) becomes more and more important with the scaling of CMOS technology and dramatic increase of power density. Performance of thermal management application is highly related to the accuracy of the temperature monitoring devices. However, due to increasing process variations and parameter drifts, temperature measurements by on-chip thermal sensors may not be accurate unless these sensors are calibrated before shipping the devices to the users. Existing calibration methods impose large time cost and cannot be used for in-field calibration. In this paper, we propose a technique to calibrate on-chip thermal sensors during manufacturing as well as in-field. We model the cyclic dependence between leakage power and temperature and perform calibrations to evaluate the calibration accuracy. Experimental results on 100 dies with different process variation parameters and three corner cases show that our technique have very high accuracy.