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Presented is a piezoresistive absolute micro pressure sensor, which is of great benefit for altitude location. In this investigation, the design, fabrication and testing of the sensor are carried out. By analysing the stress distribution on sensitive elements using the finite-element method (FEM), a novel structure through the introduction of beams into the standard bossed diaphragm is built up. The proposed configuration presents its advantages in terms of sensitivity and overload resistance compared with the standard bossed diaphragm and conventional plane diaphragm structures. The sensor is fabricated based on silicon bulk micromachining technology, and the detailed processing program is discussed. Calibration data obtained through measurements are in good agreement with the results of the FEM analysis. Testing results demonstrate that the sensor features a high sensitivity of 11.098 V/V/Pa in the operating range of 500 Pa at room temperature, and a high-overload resistance (200 times overload) to protect it from being destroyed under atmospheric environment. Owing to the excellent performance, the sensor can be applied for measuring absolute micro pressure lower than 500 Pa.