A thermopile-based sensor is fabricated using semiconductor fabrication technology and MEMS technology. The sensor is used for bio-application. When the biochemical reaction happens, the chemical reactive heat will occurs. The heat will be detected by the thermopile on the sensor. The heat will be transferred into the electrical voltage as the output signal. According to the amount of the signal and the total time of the reaction, what kind of the reaction happens and the concentration of the reactant will be known.