We studied the effect of bending on the carrier transport properties of flexible 6,13-Bis (triisopropylsilylethynyl)-pentacene (TIPS-pentacene) field-effect transistors. Results showed that the effective carrier mobility increased similar to 30% with a 1.5% mechanical strain (compressive stress), whereas it decreased similar to 15% with a - 1.5% strain (tensile stress). Theoretical analysis based on the Maxwell-Wagner model was carried out, and suggested that both carrier mobility and carrier density in the organic field-effect transistor (OFET) channel were modulated due to the mechanical strains. The microscopic electric-field-induced second harmonic generation (EFISHG) images showed that carrier transport was governed by the presence of grains of TIPS-pentacene. The EFISHG observation is a powerful tool to investigate carrier transport in flexible OFETs which are being subjected to mechanical strains. (C) 2013 Elsevier B. V. All rights reserved.