The effects of the single-event upset (SEU) generated by radiation on nanowire field-effect transistors (NW-FETs) and nanosheet (NS)-FETs were analyzed according to the incident angle and location of radiation, by using three-dimensional technology computer-aided design tools. The greatest SEU occurred when the particle was incident at 90°, whereas the least occurred at 15°. SEU was significantly affected when the particle was incident on the drain, as compared to when it was incident on the source. The NS-FETs were robust to SEU, unlike the NW-FETs. This phenomenon can be attributed to the difference in the area exposed to radiation, even if the channel widths of these devices were identical.