AbstractWe have investigated a series of α,α'-oligothiophenes with chromophore length ranging from four to six units, and with side chains comprised of ten, six, two, and zero alkyl units. We have fabricated top-contact and bottom-contact organic TFTs with thermally evaporated active layers and found that the TFT performance depends critically on the length of the side chains and on the contact configuration (with mobilities ranging from 0.07 to 1.1 cm² / V-s), but is relatively insensitive to the chromophore length. We have also fabricated ring oscillators with didecylsexithiophene and measured a signal propagation delay of 30 μsec per stage. In addition, we have fabricated oligothiophene-TFTs with ultra-thin self-assembled monolayer (SAM) gate dielectrics, with the intent to evaluate if long alkyl side chains contribute usefully to the effective thickness of a SAM gate dielectric. We have measured carrier mobilities as large as 0.05 cm² / V-s and subthreshold swing as low as 200 mV / decade.