Since early times, some kinds of semi-conductor have been known as sensitive material for magnetism in which the Hall effect occurs. Recently semi-conductor called SMD (Sony Magnetodiode) has been made and said it is more sensitive than Hall effect elements. If the direction of the earth's magnetic field is detected by SMD, the system will become simple and moreover the bearing is put out as the voltage signal. It is also possible to make repeater compass. In this paper, the theoretical and experimental investigations on the SMD is described and the possibilities for the SMD compass are informed.