In this article, a new alignment-layer approach based on block copolymers (BCPs) is proposed for mobility anisotropy and enhancement of organic thin-film transistors (OTFTs). In particular, the poly(3-hexylthiophene) (P3HT) TFT with polystyrene-block-poly(methyl methacrylate) alignment layer was studied. With max dichroic ratio 1.23 in polarized absorption spectra of P3HT and corresponding device mobility anisotropy 4.63, taking place at the highest annealing temperature of 230 degrees C, the BCP alignment approach proved to be an effective tool for orientation control of polymers such as the P3HT. However, because of negative effect of thermal annealing that causes twisting in P3HT backbones, the achieved mobility enhancement was only a meager 41%. Nevertheless, with rich varieties in the composition and complexity of BCPs, the proposed BCP alignment design represents an interesting alternative to existing alignment approaches to orientation control of P3HT and mobility anisotropy and enhancement of the resultant OTFTs. Besides, the phase-alternate surface morphology of the BCP alignment layer was confirmed through a series of atomic force microscopy, X-ray photoelectron microscopy, and field-emission scanning electron microscopy. POLYM. ENG. SCI., 52:2581-2587, 2012. (C) 2012 Society of Plastics Engineers