Ink jet printing conductive metal nanopastes have been studied in research on printed circuit boards and passive components. This technique provides a manufacturing method that can replace more expensive processes, such as lithography or metal evaporation. In this paper, we demonstrated a printed silver top-contact source-drain electrodes on bottom-gate organic thin film transistors (OTFTs). The soluble conjugated polymer, regioregular poly(3-hexylthiophene) (RR-P3HT), was used as the active channel material. To increase electric transport efficiency by tuning the surface hydrophibic characteristics, a buffer layer, V₂O₅, between organic semiconductor and printed electrodes, was introduced to resolve the incompatibility of these two layers. The results indicated the printed Ag on V₂O₅ film is hydrophilic (contact angle ∼10°), different with that on P3HT only (hydrophibic, contact angle about 65°). High hydrophilic surface of V₂O₅ led to self-aligning behavior of patterned Ag nanopastes and is helpful to get a flat film. This study also compares the characteristics of OTFTs to traditionally evaporated electrodes and to ink jet printed source-drain electrodes, in order to analyze the mechanism action of the buffer layer and its related process differences.