Hot-electron effects in plasmonic structures have been recently investigated as potential alternative mechanisms for solar energy harvesting and photodetection. [1][2][3] Hot-electron effects provide a semiconductor free route for the conversion of photons into electrical power. Here we investigate plasmonic hot electron effects in Metal-Insulator-Metal (MIM) structures using X-ray photoelectron spectroscopy (XPS). XPS has been previously used to investigate optoelectronic effects in semiconductors and nanocomposite surfaces. [4][5][6] Here, a similar approach is used to characterize the plasmonic and hot electron effects in MIM Junctions. Monochromatic Laser excitation with 450, 532 and 650 nm wavelengths are employed to illuminate the plasmonic surfaces fabricated using thermal evaporation, atomic layer deposition and electron beam lithography. The top metal of the MIM structures act as the plasmonic antenna (metal nanodiscs and gratings/stripes) that provide wavelength selective or wide band optical absorption. Plasmonic enhancement at the interface between the top metal and the insulator enhances the absorption of light in the device and leads to excitation of a larger number of hot electrons from the metal. Hot electron effects are characterized through studying the metal-insulator-metal junction and comparing shifts of binding energy belonging to the top metal islands for dark and illuminated conditions. XPS spectrum provides important information regarding the plasmonic and hot electron effects in the interface between top metal and the dielectric. A systematic study of the dependence of the XPS spectra on excitation wavelength, light intensity, polarization, insulator thickness and nanostructure geometry is presented. Effects of using different metals and insulator materials are also studied in symmetric and asymmetric tunnel junctions. Keywords: