A method and composition for removing silicon-containing sacrificial layers from Micro Electro Mechanical System (MEMS) and other semiconductor substrates having such sacrificial layers is described. The etching compositions include a supercritical fluid (SCF), an etchant species, a co-solvent, and optionally a surfactant. Such etching compositions overcome the intrinsic deficiency of SCFs as cleaning reagents, viz., the non-polar character of SCFs and their associated inability to solubilize polar species that must be removed from the semiconductor substrate. The resultant etched substrates experience lower incidents of stiction relative to substrates etched using conventional wet etching techniques.