Using X-ray diffraction-based pole figures, we present quantitative analysis of the microstructure of poly(3-hexylthiophene) thin films of varying thicknesses, which allows us to determine the crystallinity and microstructure at the semiconductor-dielectric interface. We find that the interface is approximately one fourth as crystalline as the bulk of the material. Furthermore, the use of a self-assembled monolayer (SAM) enhances the density of interface-nucleated crystallites by a factor of similar to 20. Charge transport measurements as a function of film thickness correlate with interface crystallinity. Hence, we establish the crucial role of SAMs as nucleating agents for increasing carrier mobility in field-effect devices. (C) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 611-620