Organic thin film transistors (TFTs) based on alkyl-substituted oligothiophenes with varying chromophore and alkyl side-chain length have been fabricated. The TFT performance is shown to depend on side-chain length and contact configuration, but is found to be relatively insensitive to chromophore length. Mobilities as large as 1.1 cm(2)/V s were obtained. TFTs with ultra-thin self-assembled monolayer gate dielectrics have also been prepared and investigated.