In this study, we discuss pentacene-based organic thin films grown on a self-assembled monolayer (SAM)-treated dielectric with various functional groups and molecular lengths. The functional groups and molecular lengths on the dielectric surface were modified using a SAM treatment followed by ultra violet (UV) light exposure. Surface energy was used to observe the surface polarity variation during UV light exposure. After pentacene deposition, the growth modes of pentacene on surfaces with various surface characteristics were analyzed by atomic force microscope (AFM) and X-ray diffraction (XRD). The structure of pentacene growth on different surfaces with various surface characteristics was carefully examined. Organic thin film transistors fabricated with pentacene grown on various surfaces were characterized. When the polar components of surface energy were decreased, device mobility was increased from 0.04 to 0.21 cm 2 V -1 s -1 and the threshold voltage shifted from -13.55 to -3.2 V.