We report an indium-free transparent resistive switching random access memory (TRRAM) device based on a gallium-doped zinc oxide (GZO)-Ga2O3-ZnO-Ga2O3-GZO structure grown by metal-organic chemical vapor deposition. The bipolar resistive-switching behavior is investigated based on the filament model. ZnO insulator layer fabricated at different temperature are compared to further support the filament mechanism. The compliance current applied on the device is changed from low to high to study the properties of conductive filaments in ZnO. The Joule-heating effect is also studied by adjusting the integrating time in voltage sweeping.