Poly{4,8-bis(4-decylphenylethynyl)benzo[1,2-b: 4,5-b'] dithiophene} (P1) homopolymer and poly{4,8-bis(4-decylphenylethynyl) benzo[1,2-b: 4,5-b']dithiophene-alt-thiophene} (P2) alternating copolymer have been synthesized by Stille coupling polymerization. The field-effect mobilities of both polymers were measured on both untreated and silane-treated OFET devices. Various silanes were selected to allow an incremental increase in the hydrophobicity of the silicon dioxide dielectric. A direct correlation was observed between the hydrophobicity of the silicon dioxide dielectric surface and the enhancement of the field-effect mobilities. The highest mobilities for both polymers were measured on the OFET devices treated with heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane (FS) which generated the most hydrophobic surface. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2292-2302, 2011