We present new donor-acceptor semiconducting polymers based on a strong acceptor unit, thieno[3,2-b]thiophene-2,5-dione (TTD). The polymers exhibit a deep LUMO energy level of around -4 eV while preserving a relatively low-lying HOMO energy level of below -5 eV and a quite small optical band gap of 1.2 eV. Interestingly, bottom-gate-top-contact transistor devices based on the polymers demonstrate p-channel behavior with high hole-mobilites of 1.38 cm(2) V-1 s(-1), whereas top-gate-bottom-contact devices show ambipolar behavior with hole and electron mobilities of similar to 0.12 and similar to 0.20 cm(2) V-1 s(-1), respectively. These results indicate the great potential of TTD to be used as the building unit for high-performance semiconducting polymers.