To analyze a photo-induced electron localization process at atomic step edges of the Si-native oxide interface, the time transient signal of Kelvin force microscopy with a UV laser light source was investigated. The time constant of the photoinduced process for a laser wavelength lambda = 325 nm had a linear dependence with respect to the laser power P-w. An electron transition model that takes into account photo- and thermal-effects revealed that the photo-induced localization is dominant for P-w > 0.54 mW. The small photo irradiation effect occurring at lambda = 441.6 nm is explained by the low photo absorption efficiency for visible light. (c) 2005 Elsevier B.V. All rights reserved.