A series of regioregular poly(3-alkylthiophene)s, Rg(Th-m,n/p) (m = 5, 8, 11; n = 4; p = 4, 8, 12), with alternating alkyl and semifluoroalkyl substituents has been synthesized by the GRIM polymerization method. Compared with their regiorandom analogues, Rn(Th-m,n/p), the regioregular analogues exhibit a red shift in electronic transitions in both solution and the solid state as well as considerably higher melting and crystallization temperatures. Increasing the length of alkyl side chains decreases the melting and crystallization transitions significantly. X-ray diffraction indicates that Rg(Th-m,n/p) polymers form highly ordered bilayer lamellar structures based on the assembly of the amphiphilic Janus-type structure. This supramolecular architecture can be tuned readily by varying the lengths of alkyl (p) and alkylene (m) fragments, affording interlayer distances of 40.1 angstrom for Rg(Th-5,4/4) and 57.8 angstrom for Rg(Th-11,4/8). Charge mobility was measured in organic field-effect transistors fabricated using Rg(Th-5,4/12) as the semiconductor layer. Hole mobilities of up to 1.45 x 10(-2) cm(2)/(V s) were measured in FET devices after thermal annealing of the organic semiconductor.