Desorption/ionization on silicon mass spectrometry (DIOS-MS) is a matrix-less laser vaporization method for generating gas-phase ions. The physical properties of the silicon surfaces are crucial to DIOS-MS performance and are controlled by the selection of silicon type and the silicon etching conditions. DIOS-MS has been examined for its applicability to small-molecule analysis, quantitative studies, reaction monitoring, chromatography, protein identification, and protein functional characterization. In organic chemistry, DIOS has been applied to the analysis of reactions directed toward development of new catalysts and transformations. Because DIOS offers a chip-based format, it is capable of being used to raster the silicon surface for biological and chemical screening applications, such as enzymatic activity assays. DIOS-MS extends the mass analysis capabilities of laser desorption to small biomolecules and thus offers a platform on which multiple experiments can be performed on a wide variety of molecules.