We have fabricated poly(3-hexylthiophene) organic field-effect transistors (P3HT-OFETs) with either high-temperature (200 °C) thermally cured PVP gate dielectrics or low-temperature (120 °C) photo-cured PVP gate dielectrics. We prepared the thermally cured PVP dielectric layer from a blend of poly(4-vinylphenol) (PVP) and poly(melamine-co-formaldehyde) (PMF); the photo-cured PVP dielectric formulation contained an additional photo-acid generator (PAG), which allowed the temperature for the cross-linking reaction to be reduced. We examined the intrinsic dielectric properties (e.g., the dielectric constant, the electrical insulating properties) and surface properties (e.g., morphology, surface energy) of the formulations loaded with various amounts of PAG (from 0 to 2.4 wt%). The P3HT-OFETs with the thermally cured PVP gate dielectrics exhibited an excellent carrier mobility of ca. 0.1 cm²V⁻¹ s⁻¹, a sub-threshold swing of 2.0 V decade⁻¹, and an on/off ratio of 1.2 × 10⁴. For comparison, the P3HT-OFET devices with the photo-cured PVP gate dielectrics also exhibited good electrical characteristics, including carrier mobilities as high as 0.06 cm²V⁻¹ s⁻¹, sub-threshold swings as low as 1.4 V decade⁻¹, and on/off ratios as large as 3.0 × 10⁴. To take advantage of the photo-cured PVP films, we also fabricated OFETs on a flexible, cheap ITO/PET substrate.