We introduced a facile synthetic route for well-defined [poly(3-dodecylthiophene)]2 poly(methyl methacrylate) miktoarm star copolymer (P3DDT2PMMA) by using a click reaction. For this purpose, PMMA with two ethynyl groups (PMMA-(≡)2) and ω-azidopropyl-P3DDT were synthesized. We found that a use of alkyl linker (here, propyl group) between P3DDT and azido group is very essential to minimize the steric hindrance resulting from bulky side group in P3DDT during the click reaction. When we employed a slightly excess amount of the ω-azidopropyl-P3DDT, we obtained well defined P3DDT2PMMA with a narrow molecular weight distribution (polydispersity index < 1.20) after selective removal of the unreacted ω-azidopropyl-P3DDT in a crude product by using column chromatography. We also investigated self-assembled structure of (P3DDT)2PMMA via small-angle x-ray scattering (SAXS) and transmission electron microscopy (TEM) . When the weight fraction of P3DDT block in P3DDT2PMMA was 0.48, it shows lamellar microdomains, as expected. However, P3DDT2PMMA with a wP3DDT of 0.76, we obtained hexagonally packed PMMA cylinders in P3DDT matrix, and this morphology is maintained even after crystallization of P3DDT.