We demonstrate the influence of the surface wettability of a dielectric substrate on the crystalline microstructure and film morphology of an inkjet-printed organic semiconductor, namely 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS_PEN), using various self-assembled monolayers (SAMs). Self-aligned crystals with highly ordered crystalline structure are developed by printing on hydrophilic surfaces with high surface energy. It is found that the pinning of the contact line induces an outward convective flow as the evaporation proceeds, which results in the nucleation of crystals and the self-assembly of TIPS - PEN molecules from the periphery to the central region of the droplet. However, for hydrophobic surfaces with low surface energy, small agglomerates with random orientation of molecules are formed, which is induced by depinning of the contact line. The field-effect transistors fabricated with self-organized crystals printed on hydrophilic surfaces exhibit a high field-effect mobility of 0.15 cm(2) V-1 s(-1). These results indicate that the control of both the evaporation behavior and the contact line dynamics in a drying droplet plays an important role in the printing of organic semiconductor films with uniform morphology and desired molecular orientation for the direct-write fabrication of high-performance organic transistors.