A detailed experimental investigation on nanostructured tungsten trioxide (WO3) based bottom gate field effect transistor (FET) is presented. These were fabricated using scalable process and thoroughly characterized for morphology and device performance. It was also observed that thickness of WO3 and ambient during annealing played a key role in tuning the morphology. The transistors bearing nanostructured morphology of WO3 were tested for device performance such as input-output and transfer characteristics at low, room, and high temperatures. Of all the devices tested, best on-off ratio obtained was 105 and sub-threshold slope obtained was 150 mV/decade inferring an efficient performance of the FET. A tradeoff between the on-off ratio (ION/IOFF) and sub-threshold slope was noticed at higher temperatures. This was attributed to the ambipolar nature of the WO3 films. At a given temperature and bias, either the holes or electrons were present for transport and conduction. Such ambipolar films find great potential in transistors that can be used in switching applications. © 2018 IEEE.