In this paper, we report a high-sensitivity barometric pressure sensor for use in automotive navigation, personal mobile systems and environmental monitoring. The sensor consisted of an open cavity and a micro piezo-resistive cantilever, which is placed at the cavity's opening. In the proposed structure, the cavity did not need to be vacuum-sealed and the air-gap between the cantilever and its surrounding walls was micrometer order size. The cantilever was used to detect the time-variant interaction between barometric pressure and the pressure inside the cavity. Evaluation experiments demonstrate that the sensor is able to measure the barometric pressure change with high sensitivity, with expected resolution of 0.1 Pa.