Using electric field induced optical second harmonic generation (SHG) measurement, injected carrier distribution along the channel of pentacene field-effect transistor was examined, on focusing on the region around the drain electrode. The SH was enhanced depending on applied drain-source and gate-source voltages. It was suggested that the SH enhancement reflected the distribution and amount of holes accumulated at the pentacene-SiO(2) interface. Using the Maxwell-Wagner model analysis, carrier distribution along the channel was discussed in terms of the enhanced SH intensity profile. (C) 2008 Elsevier B.V. All rights reserved.