Based on the integrated consideration and engineering of both conjugated backbones and flexible side chains, solution-processable polymeric semiconductors consisting of a diketopyrrolopyrrole (DPP) backbone and a finely modulated branching side chain (epsilon-branched chain) are reported. The subtle change in the branching point from the backbone alters the - stacking and the lamellar distances between polymer backbones, which has a significant influence on the charge-transport properties and in turn the performances of field-effect transistors (FETs). In addition to their excellent electron mobilities (up to 2.25 cm(2) V-1 s(-1)), ultra-high hole mobilities (up to 12.25 cm(2) V-1 s(-1)) with an on/off ratio (I-on/I-off) of at least 10(6) are achieved in the FETs fabricated using the polymers. The developed polymers exhibit extraordinarily high electrical performance with both hole and electron mobilities superior to that of unipolar amorphous silicon.