A theoretical analysis of plasmonic effects in a crystalline silicon-filled metallic nanohole is introduced. The dispersion properties of the guided modes of the silicon-filled silver nanohole are shown to have interesting characteristics such as negative dispersion, which is not normally observed in air-filled structures. Furthermore, the dispersion of the crystalline silicon material itself, when taken into consideration, significantly alters the dispersion characteristics of the guided modes. More interestingly, crystalline silicon is found to show metal-like properties at the edge of the UV/VIS spectrum; therefore, it is demonstrated that a silicon nanolayer surrounded by air is able to support surface plasmon polariton modes. The analysis is carried out using a full vectorial finite element method which can accurately detect the propagation properties of the structure under investigation.