Integrated circuits are inherently complicated and made more by increasing transistor quantity and density. This trend potentially enhances concomitant effects of high-energy ionizing radiation and local or impressed electromagnetic interference (EMI). The reduced margin for signal error may counter any gain in radiation hardness from smaller device dimensions. Isolated EMI and ionizing radiation studies on circuits have been extensively conducted over the past 30 years. However, little focus has been placed on the combined effects. To investigate the effect of combined EMI and ionizing radiation, two complementary metal-oxide-semiconductor inverter technologies (CD4069 and SN74AUC1G04) were analyzed for their static performance in response to both EMI and gamma radiation up to 132 krd(Si). The combined EMI and gamma radiation environment, compared to the isolated effects of each, produced the most severe degradation in inverter performance for both device technologies.