Effects of selenium substitution on [1] benzothieno[3,2b][1] benzothiophene (BTBT) on transport properties were examined by comparison of 2,7-di-tert-butyl derivatives of BTBT and newly synthesized [1] benzoselenopheno[3,2-b][1] benzoselenophene (BSBS). The single-crystal field-effect transistors of the BSBS derivative showed slightly higher mobility than that of the BTBT counterpart, which is explained by the solidstate electronic structure estimated from the packing structure elucidated by single-crystal X-ray analysis.