The invention discloses an electromagnetic heating device and mainly solves the problem that a semiconductor underlay is heated unevenly. The device comprises a heating body and a coil. The coil (5) is wrapped on the outside of the heating body (1). The heating body (1) is provided with an annular slot (6), so as to change the heat exchange direction. When the coil is electrified with alternating current, the annular slot (6) at the heating body divides the heat produced by the heating body due to induction into two parts, wherein, part of heat above the slot heats the upper surface of the heating body directly or heats the part nearby the edge of the underlay arranged on the upper surface of the heating body; the other part of heat under the slot is interdicted by the slot, so the part of heat rounds the lower part of the slot and is transmitted to the part near the center of the heating body, so as to improve the temperature distribution uniformity of the upper surface of the heating body and ensure that the heated underlay (4) is heated uniformly. The electromagnetic heating device can be used for obtaining a uniform deposition film in an MOCVD reaction chamber.