n this paper, we discuss the fabrication and characterization of pentacene-basedphototransistors using indium tin oxide as a transparent electrical gate and PMMA as a transparent dielectric gate. The photoelectric properties with different pentacene film thicknesses were characterized under ultraviolet (365 nm) illumination. We observed that for the thinner pentacene films, the threshold voltage upon UV illumination was shifted from its initial value in the dark to a positive voltage of more than 16 V, whereas the shift was only of 3 V for thicker films. Thus, we obtained a higher photosensitivity of 6.5 × 104 for thinner pentacene films, which indicates that the organic thin film transistors could find use in photodetector applications.