In this work we discuss the contacts effects in organic transistors with different architectures (staggered and coplanar). By using electrical measurements, performed at different temperatures, and numerical simulations, we show that electrical characteristics of both types of devices can be reproduced considering an effective Schottky barrier and barrier lowering at the source contact. Furthermore, we show that in staggered devices, at low V ds, the current is injected along an extended source contact region, while at high V ...