This paper present theoretical and experimental investigations on the influence of small geometries on latchup effects related to transient radiation effects. Since diffusion current due to ionizing radiation are proportional the square root of the diffusion constant and this quantity varies very little with doping concentrations considered here, useful expressions for radiation induced diffusion currents in VLSI components can be derived. Furthermore a method is presented by which electrical parameters can be measured in order to theoretically predict threshold values for radiation induced latchup.