New diketopyrrolopyrrole (DPP)-containing conjugated polymer such poly (benzothieno[3,2-b]benzothiophene-2,5-bis(2-octyldodecyl)-6-(thiophen-2-yl)pyrrolo [3,4-c]pyrrole-1,4(2H,5H)-dione) was successfully synthesized via Horner-Emmons condensation. The polymer showed a low bandgap energy (E-g = 1.56eV) in a film state. The polymer also exhibits good solubility in common organic solvents and good self-film-forming properties. The semiconducting properties of the polymer synthesized herein were evaluated in organic thin film transistors (OTFTs). The polymer exhibits charge carrier mobilities as high as 3.0 x 10(-3) cm(2)V(-1)s(-1) (I-on/off = 10(5)) after thermal annealing at 200 degrees C for 10min, which is three times higher than that of thin film transistor made of the pristine film.