Few layer graphene (FLG) samples contacted were irradiated with protons at an energy of 5 MeV and doses up to 2 X 10(15)/cm(2). The electrical properties of ungated FLG sheets contacted by Pd/Au in a source (S)-drain (D) configuration, including V-DS-I-DS, V-G-I-DS, and the hole mobility, were compared before and after proton irradiation. After irradiation, it is observed that the ambipolar conduction of the FLG sheets was changed to a p-type conduction. The field-effect mobility of the hole carriers and the resistance in the graphene sheets greatly decreased because the proton irradiation increased the number of the surface states. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3290777] All rights reserved.