The paper report the fabrication and characterization of two different sets of bottom gate top contact ZnO thin film transistors (TFTs) using SiO2 and Al2O3 dielectric layers in an attempt to compare and contrast the effect of gate dielectrics on performance of the two devices. ZnO thin film and dielectric layers were deposited at room temperature by radio frequency (RF) sputtering method. The results were validated by those obtained using commercial software tool ATLAS and an analytical model reported by others. The ZnO TFT with Al2O3 dielectric exhibited superior electrical performance as compared to the ZnO TFT with SiO2 dielectric. The study also revealed that the performance of ZnO/Al2O3 based TFTs are far more consistent and reliable as compared to their ZnO/SiO2 counterpart. © 2018 Elsevier Ltd