Abstract: Three terminal magnetic sensing devices (TTMs) having base lead layers in-plane with collector substrate materials, and methods of making the same, are disclosed. In one illustrative example, a collector substrate having an elevated region and a recessed region adjacent the elevated region is provided. An insulator layer is formed in full-film over the collector substrate, and a base lead layer is formed in full-film over the insulator layer and in-plane with semiconductor materials of the elevated region. The insulator materials and the base lead materials that are formed over the elevated region are removed. A sensor stack structure having an emitter region and a base region is then formed over the elevated region such that part of the base region is formed over an end of the base lead layer. A base conductive via may be formed to contact base lead materials of the base lead layer at a suitable distance away from the sensor stack structure.