This letter shows that degradation after pulsed stress is enhanced over comparable static stress up to a factor 10 and that it is a sensitive function of the phase shift between gate and drain voltage pulses. All our results are satisfactorily explained by the assumption that hot holes can be stored and released under certain field conditions in a layer of shallow oxide traps near the interface. The results were achieved by applying independent pulses at gate and drain. It is shown that this new method enables decisive tests of degradation models and the measurement of critical time constants.