To provide a high-sensitivity magnetic sensor which operates under a low-voltage and low-current condition.

A semiconductor magnetic sensor is constituted by providing a carrier running area 1 which is formed on a semiconductor substrate in a layered state and provides a running route for carriers, a gate electrode 5 which is stuck to part of the running area 1 in the running direction of the carriers and forms a Schottky junction with the running area 1, and detecting electrodes 4A and 4B stuck to both side-end sections of the running area 1 near the electrode 5 in a paired state, so that a Hall electromotive force may be fetched across the electrodes 4A and 4B by causing an electric field concentration in the carrier running area on the detecting electrode side in the running direction of the carriers by impressing a prescribed bias voltage upon the gate electrode 5.