Structures for a bipolar junction transistor and methods of forming a structure for a bipolar junction transistor. The structure includes a substrate having a well, a first terminal including a first raised semiconductor layer, a second terminal including a second raised semiconductor layer, and a base layer positioned in a lateral direction between the first raised semiconductor layer of the first terminal and the second raised semiconductor layer of the second terminal. The base layer has an overlapping arrangement with the well. The structure further includes a dielectric layer positioned in a vertical direction between the first terminal and the substrate, the second terminal and the substrate, and the base layer and the substrate.