Relaxor ferroelectric polymers exhibit high k at their structural phase transition around room temperature. They are particularly attractive as gate dielectric in organic field effect transistor (OFET). Nevertheless, their applications are limited due to their low thermal stability. A polymer blend system with a high and thermally stable dielectric constant is demonstrated by mixing terpolymer poly(vinylidene fluoride-trifluoroethylene-chlorofluorethylene) P(VDF-ter-TrFE-ter-CFE) with copolymer poly(vinylidene fluoride-trifluoroethylene) P(VDF-co-TrFE). PVDF-based blends of various compositions are characterized by dielectric spectroscopy, differential scanning calorimetry (DSC), infrared spectroscopy, small and wide angle X-ray scattering (SAXS and WAXS), and atomic force microscopy (AFM) in order to investigate the relationship between morphology and crystallization of the blend and their dielectric properties. An optimized blend of P(VDF-ter-TrFE-ter-CFE) [55/37/8] and P(VDF-co-TrFE) [46/54] at a ratio of 70/30 is found to exhibit a quasi-constant dielectric constant of 40 ± 2 over a wide temperature range (20–80 °C). Furthermore, electrical characteristics of the PVDF-blend-based gate dielectric OFET show further thermal stability in comparison to OFET based on high-k terpolymer P(VDF-ter-TrFE-ter-CFE) [55/37/8]. An improvement of their drain current stability by up to 60% is demonstrated at 60 °C. These findings enable broader applications of fluoropolymers in organic electronics.