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A surface-micromachined capacitive-type micro electro-mechanical system (MEMS) acoustic sensor with 0.8 μm CMOS impedance transducer is presented. This sensor chip is composed of a surface-micromachined MEMS microphone with X-shape bottom electrode anchors and a simple monolithic integrated impedance transducer based on 0.8 μm CMOS process (1 poly-2 metals), where Metal 2 in the CMOS process is also used as a bottom electrode for a sensor part. The total chip area is 0.8 mm × 0.9 mm. The Si MEMS acoustic sensor proposed in this paper has a diameter of 500 μm and a back chamber depth of 20 μm. It shows a zero-bias capacitance of 1.25 pF at 1 kHz and a pull down voltage of 33.4 V, and an open-circuit sensitivity of 0.53 mV/Pa on a bias of 9 V. In addition, the impedance transducer transfers a high output impedance to a low input impedance with a 9.5 dB gain at an input condition of 5 mV at 1 kHz.