The synthesis, characterization, and field-effect transistor (FET) properties of new indolo[3,2-b]carbazoles are described. In particular, an extensive characterization of their crystal structures has revealed the importance of the nature of the side chains (alkyl, phenyl, thienyl substituents) on their solid-state organization. These organic materials have exhibited p-type FET behavior with hole mobilities as high as 0.2 cm(2) V(-1)s(-1) with an on/off current ratio higher than 10(6). Best results were obtained with phenyl-substituted indolo[3,2-b]carbazoles since the presence of phenyl substituents seems to allow efficient overlap between the oligomeric molecules. More importantly, FET properties were kept constant during several months in air.