C60/Pentacene-based ambipolar organic heterostructure field-effect transistors (AOFETs) with Al source-drain (S/D) electrodes modified by inserting a transition metal oxide (V2O5) layer are fabricated. Compared with the device without V2O5 modified layer, the modified device shows good ambipolar characteristics with a hole mobility of 8.6× 10-2 cm2/V·s-1 and an electron mobility of 6.4× 10-2 cm2/V·s-1, and threshold voltages of 25 and -25 V, respectively. These performance improvements are ascribed to the presence of V2O5 layer at the Pentacene/Al interface which significantly reduces the source/drain contact resistance, increases the holes injection and makes electronic and hole injection close to balance. This result indicates that modified electrodes by V2O5 film is an effective approach to fabricating low cost and high performance AOFETs for realizing commercial applications.