Abstract: A study to determine the single event burnout (SEB) and single event gate rupture (SEGR) sensitivities of power MOSFET devices is carried out by exposure to fission fragments from 252 Cf source. Presented are, the test method, test results, a description of observed burnout current waveforms and a disscusion of a possible failure mechanism. The test results include the observed dependence upon applied drain or gate to source bias and effect of external capacitors and limited resistors.