The effects of electromagnetic interference with increasing frequencies from 1 MHz to 20 GHz on CMOS inverter have been studied using our two dimensional mixed-level circuit and semiconductor device simulator. The simulation results show that the channel of MOS devices could be formed or cutoff deliberately by electromagnetic interference at the lower frequency range. As a result, the normal operation of CMOS inverter is disturbed. Electromagnetic interference at the higher frequency range could couple to the output through the small intrinsic capacitances in MOS devices to upset the operation of CMOS inverter. Moreover, electromagnetic interference at the lower frequency range causes greater upsets than that at the higher frequency range.