Abstract: A semiconductor magnetic field sensor has a base region, an emitter which injects minority carriers into the base region along an injection axis, and a collector intersected by the injection axis which collects minority carrier flows. An additional pair of collectors are laterally spaced from the emitter and the injection axis to receive lateral current components arising in the base region from the injected minority carriers. Magnetic fields applied to the base cause a redistribution of the minority carriers between the lateral current components and the strength of the magnetic field can be measured by comparing the magnitudes of the resulting collector currents. Base strips on laterally opposing sides of the emitter form junctions that suppress parasitic lateral injection. Reverse biasing the junctions focuses the injected minority carriers to a greater degree along the injection axis thereby markedly enhancing device sensitivity.