Here the authors report a novel optical second harmonic generation (SHG) measurement that allows carrier motion in solids to be probed directly. By catching nonlinear polarization induced in the solids by coupling with incident electromagnetic waves (laser beam) and dc electric field from moving carriers, carrier motion is visualized. Experiments making use of time-resolved SHG technique has revealed dynamic changes of SHG intensity profiles arising from pentacene field effect transistors in accordance with the carrier transport in the channel. The observed SHG intensity profiles are strongly dependent on the physical condition of the organic field effect transistors channel and well accounts for the effect of carrier traps on gate insulator such as silicon dioxide (SiO2) and poly(methyl methacrylate). The authors anticipate that a technique using time-resolved SHG can be a powerful tool to characterize interface states of organic devices. (C) 2010 American Vacuum Society. [DOI:10.1116/1.3454371]