A novel photoresponsive organic field effect transistor (photOFET) based on naphthalene bis-benzimidazole (NBBI) by employing a transparent divinyltetramethyl disiloxane-bi (BCB) as dielectric is presented. The optical properties of naphthalene tetracarboxylic diimide (NTCDI) were changed by substitution of imidazole groups, in order to improve amplification of fabricated transistor by light in the visible region. The electrical characteristics of photOFET showed n-channel properties under illumination and dark. The NBBI based organic field effect transistor exhibited saturated electron mobility of 6 x 10(-3) cm(2)/V s with threshold voltage of 7.2 V. The photogenerated charge carriers strongly influence the drain-source current in comparison to dark condition. The photosensitivity and photoresponsivity of device are found to be 93.4 mA/W and 14.3 mA/W, respectively, at off-state of device under white light at AM 1.5 condition. (C) 2010 Elsevier B.V. All rights reserved.