Hybrid Au@In₂O₃ microstructures with a distinctive core–shell configuration have been successfully synthesized by employing Au@carbon spheres as sacrificial templates. The In₂O₃ shell can be easily decorated on the Au core by a facile aging process at room temperature (25 °C) combined with a subsequent calcination. Field emission electron microscopy and transmission electron microscopy images revealed that the Au@In₂O₃ core–shell structures had an average diameter of about 150 nm and the thickness of the porous In₂O₃ shell was ca. 50 nm. When tested as a potential sensing material for gas sensing, the resulting hybrid Au@In₂O₃ core–shell structures exhibited a higher response to formaldehyde compared with the pure In₂O₃ spheres. The enhanced sensing properties of Au@In₂O₃ core–shell structures were attributed to their intense electron depletion that arose from the catalytic activity of Au nanoparticles and the formation of metal–semiconductor junction.