A photoresponsive organic field-effect transistor was fabricated on indium tin oxide deposited onto polyethersulphone flexible substrate with pentacene as the active material and poly(4-vinyl phenol) as the dielectric material. The mobility, threshold voltage and maximum number of interface traps for the pentacene-OTFT under dark, UV and white light illuminations were found to be 2.22×10 −1 cm 2 /Vs, 12.97V, 1.472×10 13 eV −1 cm −2 and 2.93×10 −1 cm 2 /Vs,14.84V, 1.431×10 13 eV −1 cm −2 and 2.95×10 −1 cm 2 /Vs, 17.70V, 1.447×10 13 eV −1 cm −2 , respectively. The phototransistor under UV and white illuminations exhibits a high photosensitivity in the off state. The obtained results indicate that the flexible pentacene transistor could be potentially used in photodetectors by a white light and UV optical gate.