The invention relates to a sensor for measuring a magnetic field. The inventive sensor has a high level of measuring sensitivity compared to a Hall probe, comprising several electrically semiconductive layers. The layers are arranged in the form of a power diode connected in the reverse direction, consisting of an anodelayer, a cathode layer and an intrinsically conductive layer enclosed between the two. The anode layer is subdivided by insulation sections into several anode layer areas, these areas being insulated from each other. The cathode layer has an injector area on the areas opposite the insulation sections which is oppositely doped. An electron beam is formed between the injector area and the anode by applying an injection voltage to the injector area. The electron beam is distributed across the areas of the earthed anode layer areas in the form of uniform partial currents. The electron beam is diverted by a magnetic field which forms in the intrinsically conductive layer, resulting in partial currents of different strengths on the earthed anode layer areas. The magnetic field can then be evaluated by measuring these differences in strength between the partial currents.