A method includes: calculating a first calibration temperature based on a first ratio of a known external voltage to a delta voltage that is a difference between first and second base-emitter voltages of first and second sensing transistors, calculating a first sensed temperature based on a second ratio of the first base-emitter voltage to the delta voltage, adjusting one or more temperature fitting parameters based on a comparison of the first sensed temperature with the first calibration temperature; activating the on-chip heater; calculating a second calibration temperature based, at least in part, on a third ratio of the known external voltage to the delta voltage, calculating a second sensed temperature based on a fourth ratio of the first base-emitter voltage to the delta voltage, adjusting at least one of the one or more temperature fitting parameters based on a comparison of the second sensed temperature with the second calibration temperature.