Thin film transistor (TFT) has been fabricated and characterized using semiconducting polymers with and without end-capping group (polyhedral oligomeric silsesquioxanes (POSS)). These include POSS poly(2-methoxy-5-(2-ethyl-hexyloxy)1,4-phenylene vinylene) (MEH-PPV-POSS) and POSS poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine (Poly-TPD-POSS). The mobility of semiconducting polymer with silsesquioxane has large improvement, at least one order of magnitude larger than that of parent polymer without POSS. On the other hand, thermal annealing can slightly improve the field-effect mobilities of the parent polymers. (C) 2003 Elsevier B.V. All rights reserved.