A series of new organic semiconductors for organic thin-film transistors (OTFTs) using dithieno[3,2-b:2′,3′-d]thiophene as the core are synthesized. Their electronic and optical properties are investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-vis and photoluminescence spectroscopies, thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). The compounds exhibit an excellent field-effect performance with a high mobility of 0.42 cm2 V–1 s–1 and an on/off ratio of 5 × 106. XRD patterns reveal these films, grown by vacuum deposition, to be highly crystalline, and SEM reveals well-interconnected, microcrystalline domains in these films at room temperature. TGA and DSC demonstrate that the phenyl-substituted compounds possess excellent thermal stability. Furthermore, weekly shelf-life tests (under ambient conditions) of the OTFTs based on the phenyl-substituted compounds show that the mobility for the bis(diphenyl)-substituted thiophene was almost unchanged for more than two months, indicating a high environmental stability.