A macroscopic investigation of single-even-upset (SEU) trends for a class of CMOS/NMOS static RAMs exposed to heavy ions and protons has been performed. Analysis of the logical and spatial distribution of upsets as well as individual bit-upset polarity shows the need to consider the effects of peripheral circuitry interactions in understanding and modeling SEU phenomena, with important implications for spacecraft systems designs. Experimental studies and analysis of upset distributions along with SPICE modeling of the potential for word line upsets give a clear indication that upsets resulting from particle strikes on peripheral circuitry are occurring, and that the propagation of upsets along peripheral circuitry can have a serious impact on the numbers of logic word multiple upsets observed, depending on the layout of the device. >