Abstract: CMOS circuits are made resistant to erroneous signals produced by the impact of high energy charged particles (commonly known in the literature as Single Event Upset or SEU) by the addition of upset immune transistor structures into the circuits in such a way that they block and dissipate the erroneous signal. The added transistor structures are made immune to SEU by placing them in well diffusions that are separate from the rest of the circuit and biasing those wells such that the electric fields surrounding the transistors are very low in comparison to the rest of the circuit. Signal blocking is achieved with an SEU immune transistor that is in an “off” state whenever other circuit transistors that deliver signals through it are potentially sensitive to SEU. Dissipation is achieved with either a resistor or low current drive transistor that spreads the SEU signal out over time thereby reducing its voltage change to an acceptable level.