The synthesis and carrier-transport properties of oligothiophene liquid-crystalline semiconductors are reported. An asymmetrically substituted terthiophene and quaterthiophene give rise to a highly ordered smectic mesophase (see Figure) with an excellent carrier mobility of up to 0.1 cm(2) V-1 s(-1) over a wide mesophase temperature range, including ambient temperatures. Ibis mobility is comparable to that of organic polycrystals.