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In this paper, Au-modified three-dimensionally ordered macroporous ZnO:In (3DOM Au–ZnO:In) was synthesized by a one-pot method using a PMMA colloidal crystal template. The 3DOM ZnO:In with uniformly dispersed Au had large specific surface areas and highly ordered pore structures. The ethanol-sensing properties of 3DOM Au–ZnO:In were investigated and the sensor based on the 0.050 mol% Au-loaded 3DOM ZnO:In exhibited the highest sensitivity (∼240) to 100 ppm ethanol at the optimum operating temperature of 250 °C. Moreover, the fabricated sensor exhibited excellent selectivity and good stability. Therefore, the Au-modified 3DOM ZnO:In is a promising material for a novel ethanol sensor. The reason for the improvement of the sensitivity was investigated. The large surface area of the 3DOM structure was beneficial for gas adsorption and transfer, and In-doping can increase the electron carrier concentration. Moreover, Au modification enhanced the content of adsorbed oxygen, and thus resulted in a thick depletion layer and high sensitivity. [ABSTRACT FROM AUTHOR]