Abstract: A microelectromechanical system（MEMS） thermoelectric cooler is designed to be built upon a Si rim to diminish the substrate's thermal bypass. The thermoelectric thermoelements were fabricated in Bi₂Te₃ films which have the high figure of merit at room temperature. Increased reduction in size makes the cooler smaller, and the fabrication of the MEMS cooler is made compatible with microelectronics fabrication processes, so that the cooler can be easily integrated with electronic devices. The length and thickness of thermoelectric elements are optimized for achieving maximum cooling performance of the cooler. Effects of substrate thermal bypass, convection and radiation heat loads and electrical contact resistances are taken into account in the calculation. As a result, the cooling power of a few milliwatts or a maximum temperature difference of 40 K can be achieved.