 Using a magnesiothermic reduction process, the successful conversion of hierarchically organized meso/macroporous silica monoliths to self-supporting macroporous silicon networks comprising interparticle mesoporosity has been demonstrated. By careful variation of reaction time and temperature, the final network structure can be controlled to a large degree. Scanning and transmission electron microscopy images indicate that the cellular silicon structure is built up from aggregated 1–15 nm sized crystalline silicon particles aggregated to struts that form macropores of approximately 2 µm diameter.