The solubility and low processing temperatures of organic semiconductors enable fabrication of electronic devices using relatively simple printing technologies, and hold promise for realizing flexible plastic devices by environment-friendly production methods at low cost. In particular, by effectively using the self-assembling ability of molecules, production methods for organic semiconductor devices are expected to become more efficient in terms of energy and material consumption. We have developed two solution-based methods for self-organized formation of organic semiconductor crystals, including area selective nucleation of crystalline semiconductor films and direct formation of organic single crystals. These bottom-up methods of device fabrication, wherein the intrinsic functionalities of molecules are utilized for spontaneous assembly, may become a core technology for future plastic electronics.