Here we present synthesis and electronic properties of a new alternating copolymer composed of dithieno[2,3-d;2',3'-d']benzo[1,2-b;4,5-b']dithiophene (DTBDT) and diketopyrrolopyrrole units, poly dithienobenzodithiophene-co-diketopyrrolopyrrolebithiophene (PDPDBD). The resulting polymer showed hysteresis free, fast switching and highly reliable organic thin-film transistor properties comparable to a-Si. Hole mobility of the polymer is about 2.7 cm(2)V(-1)s(-1), which is remarkably improved compared with its benzodithiophene (BDT)-analougue that contains a smaller aromatic ring of BDT in the place of DTBDT. This is mainly due to much increased intramolecular charge transport originated from PDPDBD's rigid molecular backbone. Furthermore, photoconductor devices fabricated by using PDPDBD as an active layer showed a high performance with the highest photoconductive gain of ~10(5). Taken together, the successful PDPDBD's transistor and photoconductor performances with high device stability demonstrated practical applicability of PDPDBD in low-cost and flexible optoelectronic devices.