Poly(vinylidene fluoride-trifluoroethylene) (70–30 mol%) was used as the functional dielectric layer in organic ferroelectric field effect transistors (FeFET) for non-volatile memory applications. Thin P(VDF-TrFE) film samples spin-coated on metallized plastic substrates were stretch-annealed to attain a topographically flat-grain structure and greatly reduce the surface roughness and current leakage of semi-crystalline copolymer film, while enhancing the preferred β-phase of the ferroelectric films. Resultant ferroelectric properties (PR = |10| μC/cm2, EC = |50| MV/m) for samples simultaneously stretched (50–70% strain) and heated below the Curie transition (70 oC) were comparable to those resulting from high temperature annealing (>140 oC). The observed enhancements by heating and stretching were studied by vibration spectroscopy and showed mutual complementary effects of both processes. Organic FeFET fabricated by thermal evaporating pentacene on the smooth P(VDF-TrFE) films showed substantial improvement of semiconductor grain growth and enhanced electrical characteristics with promising non-volatile memory functionality.