Organic thin film transistors were fabricated using evaporated zinc phthalocyanine as the active layer. Parylene film prepared by chemical vapour deposition was used as the organic gate insulator. The annealing of the samples was performed at 120°C for 3 h. At room temperature, these transistors exhibit 𝑝-type conductivity with field-effect mobilities ranging from 0.025–0.037 cm²/Vs and a (𝐼_on/𝐼_off) ratio of ∼ 10³. The effect of annealing on transistor characteristics is discussed.