The measurement of the power dissipated by a semiconductor device is essential to evaluate the performance and reliability of power electronics systems. Power loss measurement can be difficult when the device is highly efficient and the losses are extremely low. When measuring the efficiency of an electronic system, many kind of errors can be introduced by the probes or by instruments and therefore the use of bulky and expensive set-ups are often required. The paper presents a simple method based on a heat flux measurement sensor that allows the estimation by calorimetry of the power dissipated by a semiconductor device. A control/readout circuit keeps the switching device at room temperature minimizing the heat exchanged with the ambient, improving the accuracy of the measurement.