ZnO nanoplates with hexagonal wurtzite structure were synthesized by hydrothermal treatment. The averagedimension and average thickness of the plates were $\sim 200 \times 400$ and 40 nm, respectively. ZnO nanoplates were deposited on Pt-interdigitated electrodes for the fabrication of gas-sensing devices. The ethanol-sensing properties of the devices were investigated in the dark vs. ultraviolet (UV) illumination. Under the UV illumination, the optimal operating temperature of the devices can be reduced from 237 to 164$^{\circ}$C and the response of the device was increased from 2.8 to 8.5 towards 1500 ppm ethanol vapour.