A transistor die includes input and output terminals and a source through-substrate via (TSV) between the input and output terminals. First and second primary drain contacts extend from the output terminal toward the input terminal past first and second sides, respectively, of the source TSV. An ancillary region is located adjacent to the source TSV, and boundaries of the ancillary region are defined by the source TSV, the first and second drain contacts, and one of the input terminal or the output terminal. The transistor further includes a primary transistor element, including a primary drain contact, a primary source contact, and a primary gate structure, located outside of the first ancillary region, and an ancillary transistor element, including an ancillary drain contact, an ancillary source contact, and an ancillary gate structure, located within the ancillary region.