A method for calibrating a digital temperature sensor circuit, the circuit comprising an analogue temperature sensing means, an internal reference voltage source and an analogue-to-digital converter (ADC). The ADC is arranged to receive respective signals from the analogue temperature sensing means and the reference voltage source and output a digital signal indicative of the ambient temperature. The method comprises the steps of determining the value of the internal reference voltage outputted by the reference voltage source, comparing it with the desired reference voltage value, and adjusting the reference voltage source in response to the result of the comparison step. Such an electrical voltage mode calibration can significantly reduce production costs, as it can be performed much faster than a traditional thermal calibration. The method can be applied to a sensor that produces a PTAT voltage that has to be compared to a temperature-independent bandgap reference voltage.