2,6-Diakylbenzo[1,2-b:4,5-b']diselenophenes developed as soluble organic semiconductors gave a unique molecular arrangement in bulk single crystals, where pi-stacking dimeric pairs and monomeric molecules are arranged in a similar manner to herringbone packing. Such unique structure was preserved in thin films on Si/SiO2 substrate, and the thin films fabricated by solution- or vapor-deposition acted as an active channel of field-effect transistors with mobility up to 8.4 x 10(-2) cm(2) V-1 S-1 for solution- and 2.3 x 10(-1) cm(2) V-1 s(-1) for vapor-processed devices, respectively.