An investigation is presented of the effect of the surface roughness of poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes on the growth of pentacene and the electrical performance of PEDOT electrode bottom contact pentacene transistor. Smooth PEDOT films contained well-oriented and small sized pentacene islands whilst rough PEDOT films exhibited randomly oriented islands with non-uniformly sized islands. In addition, PEDOT electrodes provided morphological continuity at the electrode-channel interface, making the accumulation channel of the pentacene formed on the electrodes a main contributor to the contact resistance. Accordingly, the smooth PEDOT surface yielded the low contact resistance (5.7 k Omega cm), approximately half of that obtained with the rough surface. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.