A Monte Carlo approach is used to obtain statistical information on the effect of the spatial distribution of the numerous secondary ions involved in neutron induced soft error rates (SER). The sorting criteria for the occurrence of upset are derived from a simplification of previous work on full-cell three-dimensional (3-D) SRAM device simulation. The time thus saved allows the treatment of a wide variety of track conditions. The shape and extension of the sensitive region is explored and correlated to the secondary ion properties. Details on the variations of the sensitivity with depth into the sensitive region as well as on the geometrical conditions associated with those tracks that cause upsets are given.