We herein report the effective performance enhancement of the pentacene-based organic thin film transistors with silicon dioxide dielectric by inserting a thin metal phthalocyanines interlayer between Au source/drain electrodes and the pentacene active layer.The threshold voltage decreased remarkably from ca.-20 V to a few volts(below-7.6 V) while the mobility increased 1.5-3 times after the insertion of the interlayer of only ca.2 nm,which could be attributed to the reduction of the carrier injection barrier.The results suggest a simple and effective way to achieve low-threshold-voltage pentacene-based organic thin film transistors with high mobility on silicon dioxide dielectric. We herein report the effective performance enhancement of the pentacene-based organic thin film transistors with silicon dioxide dielectric by inserting a thin metal phthalocyanines interlayer between Au source / drain electrodes and the pentacene active layer. The threshold voltage decreased remarkably from ca. -20 V to a few volts (below-7.6 V) while the mobility increased 1.5-3 times after the insertion of the interlayer of only ca.2 nm, which could be attributed to the reduction of the carrier injection barrier. The results suggest a simple and effective way to achieve low-threshold-voltage pentacene-based organic thin film transistors with high mobility on silicon dioxide dielectric.