We report on metal-semiconductor-metal ultraviolet photodetectors based on a ZnO film/Pt nanoparticles/ZnO film composite structure. The responsivity of the sandwich photodetector is 45 times greater for the back-illuminated than the front-illuminated. Surprisingly, the responsivity of a ZnO photodetector without the Pt nanoparticles has rather feeble enhancement under the same conditions (illumination from back and front). The responsivity of the sandwich photodetector can be enhanced from 14 to 45 times by adjusting the embedded depth of the Pt nanoparticles. Combining this result with the optical absorption spectra of ZnO films with and without Pt nanoparticles, we can reasonable to deduce the underlying mechanism and attribute it to the coupling of the localized surface plasmon from Pt nanoparticles with ZnO films. These results demonstrate a method to control the responsivity enhancement by adjusting the embedded depth of the Pt nanoparticles in the sandwich photodetector. (C) 2016 Elsevier B.V. All rights reserved.