Copper phthalocyanine (CuPc)-based thin film transistors were fabricated using CuPc films grown under different deposition pressure (Pdep) (ranging from 1.8 × 10-4 Pa to 1.0 × 10-1 Pa). The transistor performance highly depended on Pdep. A field-effect mobility of 2.1 × 10-2 cm2/(V s) was achieved under 1.0 × 10-1 Pa. Detailed investigations revealed that P dep modulates the molecular packing and orientation of the organic films grown on a SiO2/Si substrate and influences the charge transport. Furthermore, from a device physics point of view, contact resistance of the fabricated transistors decreased when Pdep increased, which was beneficial in reducing energy consumption.