A new poly(octathiophene) based copolymer was designed and synthesized by the palladium catalyzed Suzuki coupling reaction. The structure of the newly obtained copolymer was confirmed by 1H-NMR and IR. The number-average molecular weight (M(n)) of the polymer was 36,000 with a poly-dispersity index of 1.15. The polymer has good solubility in common solvents such as chloroform, toluene, chlorobenzene, dichlorobenzene and tetrahydrofuran at room temperature. The optical, thermal and electrochemical properties of the polymer were characterized by UV-vis absorption, TGA and DSC and cyclovoltametry, respectively. A thin film transistor using the new polymer as an organic semiconductor was found to exhibit typical p-channel FET characteristics with a hole mobility of 5 x 10(-4) cm2/Vs.