Thieno[3,4-c]pyrrole-4,6-dione (TPD) containing copolymer semiconductors P1-P3 were strategically designed and successfully synthesized. Their physicochemical properties were thoroughly investigated. All polymers exhibited good solution processability and high humidity stability in thin film transistors (TFTs). Transistor electrical characterization showed the device performance was sensitive to the alkyl chain substituent orientations of the polymers. A maximum TFT hole mobility of similar to 1.29 cm(2)/(V s) was observed for P3-based devices, a recorded mobility for TPD containing polymer semiconductors reported to date. The corresponding thin-film morphologies and polymer chains packing were investigated in detail by AFM and 2D-GIXD to correlate with the alkyl orientation dependent carrier mobility of P1-P3. Experimental results showed the alkyl chain orientations determined the polymer, chains packing pattern in the thin films, the film morphologies, and the resulting device performances of P1-P3.