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The fabrication of p-type vertical organic field-effect transistors (VOFETs) based on a reduced graphene oxide (rGO) electrode is a big challenge. Due to the insufficient injection barrier at the rGO/p-type organic semiconductor heterojunction, the current on/off ratio of the device is usually poor. To improve device performance and enable its application in future organic complementary circuits with their n-type counterparts, different types of interfacial layers were explored in this study. Results suggest that the highest occupied molecular orbital level and the surface morphology of the interfacial layer play an important role in device performance, while the hole mobility of the interfacial layer has less impact. In addition, the effect of the interfacial layer thickness was systematically investigated, indicating that an ultrathin interfacial layer was preferred in terms of the on-current density. Notably, the device with a 1 nm thick C60 interfacial layer gave the best device performance, exhibiting the highest current on/off ratio exceeding 5 × 103 and a maximum current density over 30 mA/cm2 under an operation voltage of −3 V. This is the first p-type VOFETs based on the work-function-tunable rGO electrode, which may open the door to rGO-based organic complementary circuits. [ABSTRACT FROM AUTHOR]