A semiconductor device including a circuitry, a magnetic sensor, and a buried oxide. The circuitry is formed on a substrate. The magnetic sensor has a sensing area formed under the circuitry. The buried oxide is disposed between the circuitry and the magnetic sensor. The sensing area comprises an N-doped area and a P-doped area doped deeper than the N-doped area, and sensor contacts connect the sensing area with the circuitry through the buried oxide.