The temperature-mediated crystal structures of N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13) on organo-compatible polymer/SiO2 bilayer dielectrics, including either physisorbed or grafted polystyrenes (PSs), were examined and correlated with their electrical characteristics in organic field-effect transistors (OFETs). The crystallinity of the PTCDI-C13 films on these dielectrics increased with increasing annealing temperature (TA), but the semiconductor–dielectric interfaces were also changed depending on the surface properties of the polymeric dielectrics. When TA was increased above the glass transition temperature of PSs, the 20–30 nm thick physisorbed PS layers became softened and further dewetted from the oxide surfaces, resulting in the subsidence and disconnection of PTCDI-C13 crystal grains into the undulated PS layers. In contrast, the PS monolayer grafted to the SiO2 surface could maintain a wetting layer even at TA = 200 °C, resulting in a hydroxyl free dielectric surface...