Highly oriented pyrolytic graphite treated with NaOH solution was found to form a stage-8 intercalation compound. Superstructures such as 2x2, √3×√3 and noble orthorhombic lattices were observed on the surface, as previously observed on the surfaces of the stage-1 M-GIC (graphite intercalation compound, M=Li, K, Rb, Cs). On the contrary, substrate lattice structure was observed on NaOH-treated MoS₂. In addition, new structures near the Fermi level were found to be formed by NaOH-treatment on the surface.