The synthesis and field-effect transistor (FET) properties of a novel class of indolocarbazolebased conjugated polymers, poly(indolo[3,2-b]carbazole)s, are described. Dehalogenative coupling polymerization of dichloroindolo[3,2-b]carbazoles with Zn/ NiCl2/ PPh3/2.2'-dipyridil gave the corresponding poly(indolo[3,2-b]carbazole)s, while oxidative coupling polymerization of indolo[3,2-b] carbazoles with FeCl3 proceeded regioselectively, affording poly(indolo[3,2-b]carbazole-2,8-diyl)s. Crystallization and optical properties of these polymers were different, depending on the regiochemistry of backbone linkages and peripheral substitutions. Thin film transistor devices using these polymer semiconductors exhibited p-channel FET behavior, dictated predominantly by nature of substitution and backbone linkages (2,8-or 3,9-linkage). Solution-processed polyindolo[3,2-b]carbazole thin-film semiconductors obtained from FeCl3 polymerization generally provided better FET performance.