New thiophene- and selenophene-fused aromatic compounds were successfully developed as high-performance semiconducting materials for organic field-effect transistors (OFETs). Among them, the most advanced compounds designed on consideration of structure-function relationship showed durable air-stable FET performance. This article highlights the research strategy and development of these superior compounds as well as the molecular factors for the improvement of mobility, sensitivity, and stability, which are very informative for the design of practical semiconductors.