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This paper presents the design, modeling, fabrication, and characterization of CMOS microelectromechanical-systems-based thermoelectric power generators (TPGs) to convert waste heat into a few microwatts of electrical power. Phosphorus and boron heavily doped polysilicon thin films are patterned and electrically connected to consist thermopiles in the TPGs. To optimize heat flux, the thermal legs are embedded between the top and bottom vacuum cavities, which are sealed on the wafer level at low temperature. A heat-sink layer is coated on the cold side of the device to effectively disperse heat from the cold side of the device to ambient air. The peripheral cavity is designed to isolate heat from the surrounding silicon substrate. Both simulation and experiments are implemented to validate that the energy conversion efficiency is highly improved due to the aforementioned three unique designs. The device has been fabricated by a CMOS-compatible process. Properties of thermoelectric material, such as the Seebeck coefficient, electrical resistivity, and specific contact resistance are measured through test structures. For a device in the size of 1 cm2 and with a 5-K temperature difference across the two sides, the open-circuit voltage is 16.7 V and the output power is 1.3 ??W under matched load resistance. Such energy can be efficiently accumulated as useful electricity over time and can prolong the battery life.