A semiconductor pressure sensor of this invention is intended to provide a semiconductor pressure sensor having an excellent electrical isolation between the supporting means of the semiconductor pressure sensor and the semiconductor substrate, the semiconductor pressure sensor basically comprising a semiconductor substrate having a first semiconductor region in which; at least a semiconductor device is formed, a second semiconductor region and an isolated layer buried between the first and second semiconductor regions, a cavity provided in the second semiconductor region, the opening thereof existing on the mail surface of the second semiconductor region and a strain detecting portion consisting of the semiconductor device and provided in the first semiconductor region opposite to the cavity. The semiconductor pressure sensor is featured in that at least one of the outer peripheral side surfaces of the first and the second semiconductor regions is formed inside of the outermost peripheral side surface of the isolation layer.