A method has been proposed for the determination of energetic distributions of localized states in organic semiconductors by the analysis of the impedance spectra (T. Okachi, T. Nagase, T. Kobayashi, and H. Naito, Appl. Phys. Lett. 94 (2009) 043301). High energetic resolution of the method is demonstrated experimentally in organic semiconductor diodes using a polyfluorene derivative, poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine), by detecting a structured localized-state distribution. The method is a powerful tool for the determination of energetic distributions of localized states with high energetic resolution in organic thin film devices such as organic light-emitting diodes and organic solar cells. (C) 2013 Elsevier B.V. All rights reserved.