Porous silicon (PS) has been formed by electrochemical etching of p-type silicon. During drying in air the sponge-like structure of the porous layers is exposed to capillary forces which will partially destroy the microstructure of highly PS. One possibility for avoiding the partial structural collapse is by supercritically drying the PS. This technique is already known from the formation of highly porous aerogels and has now been applied to PS. Porosities of 90% can be achieved. These highly porous layers were investigated using photoluminescence, Raman, reflectance and X-ray photoemission spectroscopy. The porosity was determined by gravimetric measurements. The effect of the drying process on the properties of PS was also studied.