Organic-inorganic perovskites are extremely promising as the semiconductor for high-performance field-effect transistors because of their solution processability, flexibility, and excellent carrier transport. However, their true performance remains obscured by low perovskite quality, high carrier trap density, and large contact resistance. We fabricated a perovskite layer by spin coating on a substrate treated with a self-assembled monolayer. This surface treatment led to better-developed perovskite films with lower carrier trap density. Additionally, utilizing a top-contact/top-gate structure with hole injection layers was essential for attaining smaller contact resistance and further reducing carrier trap density. By combining these methods, we realized greatly improved hole mobilities of up to 15 cm2 V"1 s"1, which is about six times the previous record hole mobility and also a top-dass value when compared with widely investigated organic transistors. We also demonstrated that this surface treatment leads to a negligible hysteresis.