Time to breakdown (tBD) of silicon dioxide has a pronounced frequency dependence when it is measured under bipolar bias conditions. At high frequencies, bipolar tBD can be enhanced by two orders of magnitude over the tBD obtained using dc or unipolar pulse bias of the same frequency and electric field. The lifetime improvement is attributed to detrapping of holes. At high frequencies, the improvement is maximum because the trapped holes are concentrated at the interface where they can easily be removed upon field reversal. At low frequencies, the improvement is less because the trapped hole distribution extends further into the oxide. Two different mechanisms are proposed to explain the frequency dependent spreading of the trapped hole distribution away from the interface.