A bis-fused donor composed of dimethyl-tetrathiafulvalene and tetraselenafulvalene (DM-ST-STP) was successfully synthesized. X-ray structure analysis of the salts with PF6- and AsF6- anions revealed that the molecular packing could be classified as beta-type. A tight-binding band calculation suggested these salts had a quasi-one-dimensional Fermi surface. They exhibited high conductivity of sigma(rt) = 390-540 S cm(-1) and metallic behavior down to low temperature.