An iterative and time-dependent simulation method based on a full band Monte Carlo algorithm is presented to describe the injection behavior of hot electrons and holes during program and erase of Twin Flash™ memory cells. Secondaries during programming and the feedback of already injected and trapped charge carriers in the ONO nitride on subsequent injection processes are taken into account. By this method it is possible to obtain valuable information on the time-dependent evolution and the local distribution of injection currents and trapped charges in the ONO nitride of the Twin Flash™ cell.