Transient radiation response for microcircuit PN junctions with enhanced photocurrent models are calculated using two-dimensional numerical simulation. On the basis of Wirth-Rogers photocurrent models, the enhanced models include two additional effects as high injection effects on excess minority carrier lifetime and electric fields in the substrate (quasi-neutral regions). These effects are most pronounced in high resistivity material. An excellent evaluation approach is provided for accurate prediction of transient response of modern microcircuit pn junctions to ionizing radiation.