The correlations between morphological features and field-effect properties of poly(alkoxyphenylene-thiophene) thin Langmuir-Schafer film deposited on differently terminated gate dielectric surfaces, namely bare and methyl functionalized thermal silicon dioxide (t-SiO2), have been systematically studied. The film morphology has been investigated at different film thickness by Scanning Force Microscopy. Films thicker than a few layers show comparable morphology on both dielectric surfaces while differences are seen for the ultra-thin polymer deposit in close proximity to the substrate. Such deposit is notably more heterogeneous on bare t-SiO2, while a more compact and uniform nanogranular structure is observed on the silylated t-SiO2. As to the field-effect properties, the methyl-terminated gate dielectric surface leads to a two order of magnitude mobility enhancement along with a field-effect thickness independent conductance. (c) 2007 Elsevier B.V. All rights reserved.