We have developed a method for integrating n- and p-type organic thin-film transistors (OTFTs) on the same substrate. An integrated shadow mask was used for the n- and p-type semiconductor patterning. The integrated shadow mask can be aligned with submicron accuracy relative to the OTFT substrate. This allows for the integration at transistor level of n- and p-type OTFTs on the same substrate. A complementary inverter was fabricated, showing excellent performance while operating at a supply voltage of 2 V.