Light-induced dry etching of Si(100) in the VUV range using synchrotron radiation (SR) and a halogen-containing gas (XeF 2 ) has been investigated with respect to selectivity, anisotropy, quantum efficiency, optimal wavelength, spatial resolution and quality of the photochemical etching processes. Microstructuring of Si with XeF 2 can be optimized to achieve etched structures in the sub-micrometre range by increasing the contrast in choosing a wavelength with minimal unselective etching. The strength of unselective etching is strongly wavelength dependent and follows the XeF 2 gas phase absorption coefficient. Fragments from dissociation of the XeF 2 reach the Si surface and thus cause unselective etching. Optimal dry etching occurs for wavelengths around 120 nm because the selectivity is high due to an excitation of a surface layer and also the quantum efficiency is very large. An efficiency of 10 removed Si atoms per incoming photon, which exceeds that in the visible spectral range by more than four orders of magnitude, combined with the higher spatial resolution at 120 nm compared to the conventional excimer laser and I-line wavelengths and the availability of optical materials for imaging present a perspective for generating line densities in the Gbit range.