Abstract: A GTO switch is provided in which the upper base layer (gate) is formed by a diffusion step. An epitaxial layer grown over the upper base layer contains cathode and gate diffusions which are separated by an undiffused gap. This "buried base" technique provides precise control over the resistivity of the base. The cathode-gate gap provides increased reverse gate voltage capacity. Other features include a large anode short area and a double-layer-metal; contact structure on the cathode-gate surface.

Abstract: An improved semiconductor device, particularly a gate controlled switch is provided by optimally fitting an involute spiral cathode-gate structure into a substantially square device. 4N cathode-gate branches radiate from a central gate portion and intersect the perimeter of the square device region at predetermined locations, N per side, where N is an integer. Four of the branches tangentially intercept the square perimeter at a distance R from a centerline where R is the radius of the central gate portion. The origin of the branches is angularly displaced from the line connecting the die center to the tangential intercept point by (L/R)- arctan (L/R) radians where L is half the edge length of the square device region. Improved thermal performance is obtained by thermally coupling the cathode heat spreader to the gate as well as cathode portions of the device.

Abstract: A semiconductor thyristor device having a cathode region and an anode region comprises ballast means adjacent thereto. The device further comprises first and second electrode means which are positioned such that only the cathode region and the anode region respectively are contacted thereby. The present structure is compatible with conventional device structures.