We report the synthesis, characterization, and OFET and OPV properties of a series of novel naphthodithiophene (NDT3)-based donor-acceptor semiconducting polymers. A striking feature of the present polymers is the very close π-π stacking of 3.5 Å, most likely as a result of the large π system and the D-A system in the polymer backbone. PNDT3NTz-DT, in particular, is found to be one of the few examples of versatile polymers that exhibit both the field-effect mobility of ∼0.5 cm2/(V s) and the PCE of ∼5%. These results indicate that NDT3 is a promising versatile core unit for semiconducting polymers and that the use of highly π-extended heteroarenes as both the donor and the acceptor unit is a promising design strategy to develop high performance polymers.