Ni nanodots (NDs) used as nano-scale top electrodes were formed on a 10-nm-thick Si-rich oxide (SiO$_{mathrm{x}}$)/Ni bottom electrode by exposing a 2-nm-thick Ni layer to remote H$_{2}$-plasma (H$_{2}$-RP) without external heating, and the resistance-switching behaviors of SiO$_{mathrm{x}}$ were investigated from current-voltage ( extit{I--V}) curves. Atomic force microscope (AFM) analyses confirmed the formation of electrically isolated Ni NDs as a result of surface migration and agglomeration of Ni atoms promoted by the surface recombination of H radicals. From local extit{I--V} measurements performed by contacting a single Ni ND as a top electrode with a Rh coated Si cantilever, a distinct uni-polar type resistance switching behavior was observed repeatedly despite an average contact area between the Ni ND and the SiO$_{mathrm{x}}$ as small as $sim$ 1.9 $ imes$ 10$^{-12}$cm$^{2}$. This local extit{I--V} measurement technique is quite a simple method to evaluate the size scalability of switching properties.