Ambipolar pentacene transistors in bottom contact-bottom gate geometry are fabricated on flexible substrates using parylene as a dielectric and self-assembled monolayer treatment of the source-drain electrodes to improve charge injection. Hole and electron mobilities of 0.07 -0.1 cm(2) V-1 s(-1) and 0.01-0.04 cm(2) V-1 s(-1) are achieved. CMOS-like inverters are built and gains of up to 110 are reported.