High-dielectric constant (kappa) materials have been extensively investigated for several potential applications, particularly in low-voltage-operating organic field-effect transistors (OFETs). To ensure the operational stability of the OFET, the interface between the organic semiconductor and the high-kappa dielectric should be fully controlled. In the current work, we overcoated a fluorinated polymer, namely poly(pentafluorostyrene) (PFS), onto one of the high-kappa materials, namely barium titanate (BaTiO3), and used this bilayer to fabricate highly stable OFETs. The surfaces of the BaTiO3 dielectric layers were effectively modified with the PFS overcoating. Compared to the uncoated BaTiO3, the PFS/BaTiO3 bilayer dielectric showed significantly reduced leakage current and altered surface properties. The smoothness of the surfaces of the PFS/BaTiO3 films appeared to have been responsible for the observed improved crystal structures of the overlying pentacene molecules. In addition, the surface dipoles and electron-withdrawing character of the PFS/BaTiO3 films built a high hole injection barrier between the semiconductor and dielectric layers, with this barrier blocking hole trapping. Finally, overcoating BaTiO3 with PFS allowed the resulting PFS/BaTiO3 to be utilized as a gate dielectric layer for highly stable OFETs during low-voltage operation. These OFETs exhibited hysteresis-free transistor performances and reliable operation under a sustained gate-bias stress in air.