We investigate the initial molecular growth of the pentacene and the corresponding transistor performance by varying the exposure angle of linearly polarized ultraviolet (LPUV) light on a poly(methylmethacrylate) (PMMA)-based photo-reactive insulator. Based on the optically verified alignment features of pentacene molecules on the LPUV illuminated PMMA-based insulator, it is found that the initial size and the anisotropy of pentacene grains are gradually increased and finally saturated with increasing the exposure angle of the LPUV light. In such situation, the resultant electrical performance of the pentacene-based organic transistor are found to be monotonically enhanced up to a certain maximum at an optimal exposure angle of 30 degrees and finally saturated. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.