Recently, metal oxide semiconductors have attracted the research community because of their highly appreciable optoelectronic properties, which made them more suitable for many device applications such as super capacitors, solar cells, gas sensors, photocatalysts, light emitting devices, and so on. [1-5] As a further development it was observed that coupling of two metal oxide semiconductors with different bandgaps improved their physical and chemical properties by affecting their electron-hole pair. These improved physical and chemical properties equipped many of the composite metal oxide semiconductors to act as good gas sensors. For instance, Chesler et al. concluded in their report that ZnO-SnO 2 composite sensor showed an increased sensor response (SR) toward CO than the pristine oxides. [6] In addition, Zhao et al. reported that the ZnO-SnO 2 heterostructures showed enhanced selectivity and response toward NO 2 and ethanol when compared with pure ZnO nanowire. [7] Furthermore, Mondal et al. said that the ZnO-SnO 2 composite thin film sensor showed enhanced sensing property over ZnO sensor. [8] Furthermore, Wang et al. reported that the ZnO/CuO composite-based sensor exhibited a superior response to H 2 S at low operating temperature. [9] It is known that our atmosphere is surrounded by numerous kinds of natural and artificial chemical gases. Some of them are essential and some others are harmful to our life. Ammonia (NH 3) is one among the various harmful gases. NH 3 is a colorless toxic gas with a pungent smelling, and long-term exposure and inhalation to higher concentration lead to serious health problems such as laryngitis, tracheobronchitis, bronchopneumonia, and pulmonary edema. Also, the existence of NH 3 in the exhale breath of people acts as a biomarker for some disease. [10] Early detection of NH 3 is a great concern to counter the accidental threats.