Self-assembled monolayer field-effect transistors (SAMFETs) of BTBT functionalized phosphonic acids are fabricated. The molecular design enables device operation with charge carrier mobilities up to 10-2 cm 2 V-1 s-1 and for the first time SAMFETs which operate on rough, flexible PEN substrates even under mechanical substrate bending. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.