Strategically functionalized 5,11-dialkylindolo[3,2-b]carbazoles (see Figure) represent a novel class of high-mobility p-channel semiconductors for organic thin-film transistors. Specifically, 2,8-dichloro-substituted 5,11-didodecylindolo[3,2-b]carbazole, which forms highly crystalline films with large interconnecting terrace-like layered domain structures, has exhibited mobilities reaching 0.14 cm(2) V-1 s(-1) and current on/off ratios of 10(7) under ambient conditions.