Increased heavy ion single-event upset (SEU) sensitivity of radiation-harden 65-nm dual interlocked cell (DICE) static random access memory (SRAM) is observed after total ionizing dose (TID) irradiation. The mechanism of the increased SEU cross section is analyzed by cell stability testing and TCAD simulation. Cell stability testing result shows that static noise margin of the cell is diminished by TID-induced threshold voltage shifts. Critical charge inducing SEU is reduced in TID-irradiated cell, because it is more susceptible to noise. Moreover, charge sharing of 65-nm DICE SRAM is a function of TID. TID-enhanced NMOSFET and PMOSFET charge sharing under heavy ion track in n-well is proposed and verified by TCAD simulation. The resistor of ground contacts of p-well is increased by positively charged oxide trapped charges induced by TID. More electrons are collected by NMOSFET owing to the more server well collapse induced by the raised resistor of ground contacts. Critical charge inducing SEU is reduced, and more carries are collected in TID irradiated device, so that the SEU sensitivity of 65-nm DICE SRAM is increased by TID.