Stress Induced Leakage Current (SILC) is one of the major problems found in ultra-thin oxides before the onset of soft or catastrophic breakdown during accelerated life tests. Quite often SILC is measured after constant current (CCS) or constant voltage (CVS) stresses, even though during the device life the operating conditions usually involve alternating, non-constant gate bias. Relatively few works are focused on this point [1]; the present contribution is one of the first addressing the problem of SILC produced by Pulsed Voltage Stress (PVS). Results have been compared with those obtained after CVS, as a function of injected charge and pulse frequency. We have also studied Radiation Induced Leakage Current (RILC) with either pulsed or constant bias voltage applied during irradiation.