A method and apparatus are provided for calibrating digital thermal sensors. A processor chip with a plurality of digital thermal sensors receives an analog voltage. A test circuit coupled to the processor chip receives a clock signal and a register coupled to the test circuit outputs a value on each clock cycle to a digital thermal sensor in the plurality of digital thermal sensors. The digital thermal sensor transitions an output state in response to the value of the register received in the digital thermal sensor equaling a temperature threshold of the digital thermal sensor. The value of the register at the point of transition is used to calibrate the digital thermal sensor. An incrementer increments the value of the register on each clock cycle in response to the value of the register received in the digital thermal sensor failing to equal the temperature threshold of the digital thermal sensor.