The crystallization and microstructure change of self-organization and the related conduction mechanisms of polymer semiconductor active thin layer in polymer organic field-effect transistors (OFET) are investigated by synchrotron radiation grazing incident X-ray diffraction (GIXRD) for understanding the relationships between polymer self-organization and charge carry. The change of the crystalline microstructure of RR-P3HT clarifies the effect of SAMs for improving the interface between the insulator layer and the organic semiconductor layer. The self-organiztion of RR-P3HT modified by SAMs improves the crystalliztion to pack form the thiophene rings along the perpendicular direction of substrate and results in that the π-π interchains are stacked to parallel the substrate. The two-dimensional charge transport is improved. Furthermore, we find that two-dimensional, conjugated, and self-organized crystalline lamellae are easier to gain with slow grown film than with fast grown film.