A novel process for fabricating alignment-free, printable, organic thin-film transistors is presented. This process exploits a self-assembly phenomenon in which soluble nanomaterials such as metal nanoparticles and organic molecules are self-assembled into a device structure. To demonstrate this process, solution-processed source and drain electrodes were self-aligned to a gate electrode by using a hydrophobic self-assembled monolayer (SAM) optically patterned onto the gate electrode with a back-substrate exposure technique. An organic semiconductor film deposited on the patterned SAM was selectively ordered and substantially self-aligned to the gate electrode. A field-effect mobility of 0.15 cm2/Vs and on/off current ratio of 105 were experimentally demonstrated when pentacene molecules were used as the semiconductor and silver nanoparticles were used as electrode materials.