Solid state gas sensors have proved to be very promising for monitoring the emission of air pollutant and toxic gases because they are a low cost element. Zinc oxide (ZnO) is II-VI compound semiconductor with a wide direct band gap of 3.37eV and a hexagonal structure. ZnO is often used in photovoltaic, gas sensor application, varistors, surface acoustic wave devices, electric transducers, piezoelectric materials and room temperature ultraviolet lasing.The objectives of this project are to study the structural, electrical and gas sensing properties of undoped ZnO thick films, to study the relationship of doping with structural, electrical and gas sensing properties of doped ZnO films with Cr2O3, Nb2O5, Al and Cu as a dopant.