A thyristor based semiconductor device includes a thyristor having cathode, P-base, N-base and anode regions disposed in electrical series relationship. The N-base region for the thyristor has a cross-section that defines an inverted “T” shape, wherein a buried well in semiconductor material forms is operable as a part of the N-base. The stem to the inverted “T” shape extends from the upper surface of the semiconductor material to the buried well. The P-base region for the thyristor extends laterally outward from a side of the stem that is opposite the anode region of the thyristor, and is further bounded between the buried well and a surface of the semiconductor material. A thinned portion for the N-base is defined between the cathode region of the thyristor and the buried well, and may include supplemental dopant of concentration greater than that for some other portion of the N-base.