WO₃ thin films deposited using a simple method of vacuum evaporation has been investigated for their NH₃ sensing properties. Effect of process parameters namely operating temperature, film thickness and amount of Au in the WO₃ host matrix have been investigated and correlated with the observed sensitivity values to obtain the optimum sensor with improved sensing characteristics towards NH₃. Pure WO₃ films with thickness of 600 nm and the Au incorporated WO₃ containing 0.034 wt.% Au were observed to exhibit a superior sensing property towards NH₃.