The organic semiconductor DNTT (dinaphtho-[2,3-b:2',3'-f]thieno[3,2-b] thiophene) and its didecyl- and diphenyl derivatives C10-DNTT and DPh-DNTT [1-3] have recently shown exceptionally large field-effect mobilities together with excellent air stability . Here we present a detailed analysis of the mobility, contact resistance, air stability and signal delay (measured in unipolar as well as complementary ring oscillators) of low-voltage (∼3 V) thin-film transistors (TFTs) based on these semiconductors with channel lengths down to 0.5 μm on flexible plastic substrates. The TFTs were fabricated with an inverted staggered device structure and with Al gate electrodes, a gate dielectric composed of a plasma-grown AlOx layer (3.6 nm thick) and a tetradecylphosphonic acid self-assembled monolayer (SAM), a vacuum-deposited organic semiconductor layer (25 nm), and Au source and drain contacts . The fabrication of organic TFTs with channel lengths as short as 0.5 μm was accomplished using high-resolution silicon stencil masks [6,7]. All measurements were performed in ambient air.