Nonuniformity of charge trapping in SiO2 after gate injection stress was investigated by a combination of wet etching of SiO2 film and oxide surface topography by atomic force microscopy. For the SiO2 subjected to the gale injection stress, microroughness during wet etching changed. That is, the change in the root mean square (Delta rms) of the oxide surface topography increased, kept constant, and decreased with decreasing oxide thickness during step etching. From peak-to-valley and Delta rms profiles of SiO2 after thermal annealing, we conclude that the increase of Delta rms values of the stressed SiO2 is due to the trapped electrons, while the decrease of them is due to the trapped holes. Basing on these results, we can know also that the trapped holes are not only distributed near an Si/SiO2 interface but also uniformly distributed in depth in the region from a beginning position of impact ionization to the Si/SiO2 interface. (C) 2001 The Electrochemical Society. All rights reserved.