In this paper, we report an investigation of barrier height change in gate oxide caused by charge injection. By analyzing the small change in the post-stress Fowler-Nordheim (FN) tunneling current through the oxide layer, the change of the oxide barrier height due to charge injection is determined quantitatively. The barrier height changes associated with different charge-injection directions and measurement polarities for n-channel metal oxide semiconductor field-effect transistors (MOSFETs) are presented. For comparison a measurement on a p-channel MOSFET is also carried out. For all the cases, the barrier height changes always exhibit a power law dependence on injected charge. (C) 2002 The Electrochemical Society.