Fabrication process technologies for Si nano-wall arrays were developed to provide samples that enable us to study the bandgap widening by the quantum confinement effect of a two-dimensional Si /SiO2 quantum well. We studied dry etching based and anisotropic wet etching ( AWE) based processes for making the nano-wall structure, and demonstrate that the AWE with KOH was applicable to the nano-wall fabrication. The obtained Si nano-walls embedded in SiO2 had vertical flat sidewalls at the interface, and 1.5 nm-wide Si walls with height of 1 to 2 mu m was formed. We expect that the bandgap widening is demonstrated by these samples. The optical reflectance of the nano-wall arrays were measured in the wavelength range of 400 nm-1000 nm, and the measured results showed that the reflectance was small as compared with that of the flat bare wafer. (C) 2017 The Electrochemical Society. All rights reserved.