We investigated the reversible resistive switching of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) thin films sandwiched between Al electrodes. The J-V sweep curve showed a hysteretic behavior which depends on the polarity of the applied voltage bias. From the analysis of I-V curves, it was revealed that the charge transport through the junction was governed by the bulk space-charge-limited conduction (SCLC) model. Using transmission electron microscopy (TEM) analysis, it was confirmed that the initial high resistance state of PEDOT:PSS films is related with the segregation of PSS chains induced by redox reaction between a Al metal electrode and PEDOT:PSS film. Positive space charges present on the top region of PEDOT:PSS films can be proposed as a possible trap centers of electron trapping and detrapping process. (C) 2009 Elsevier B.V. All rights reserved.