Poly{2,6-bis(3-dodecylthiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene] (PTBT) was synthesized, via oxidative polymerization by oxidative agent (FeCl3). The mole ratio of FeCl3 and monomer (3.5: 1), and keeping low temperature during the dropping of diluted catalyst were very important for the polymerization without crosslinking. The PTBT was confirmed by H-1 NMR, FTIR spectra, and elemental analysis. The PTBT has very good solubility in organic solvents such as chloroform, tetrahydrofuran, etc, and good thermal stability with T-g of 164 degrees C. The PTBT shows UV-optical absorption at 406 nm and photoluminescence (PL) spectroscopy at 504 mn in a film. The highest occupied molecular orbital (HOMO) energy of the polymer is -5.71 eV by measuring cyclic voltammetry (CV). A solution-processed polymer thin film transistor device shows a mobility of 3 X 10(-5) - 8 X 10(-5) cm(2) V-1 s(-1), and an on/off current ratio of 10(4). (c) 2007 Wiley Periodicals, Inc.