Aluminum passivation in silicon-doped KOH solutions has been observed and investigated using mostly Raman spectroscopy of the bulk KOH solution and the aluminum film surface. The bulk solution Raman spectra suggest that in the nonpassivating solutions silicate monomer and dimer are dominant ionic species while in the aluminum passivating solutions silicate polymers of higher order are dominant. Aluminum film etch rates in the silicon-doped KOH solutions show similar functional dependence on silicon dopant concentration as the aluminum etch rate in silicon-doped tetramethylammonium hydroxide solutions. Silicon etch rate decreases dramatically with increasing silicon dopant concentration in KOH solutions. Rationale is suggested explaining the lack of previous observation of aluminum passivation in silicon-doped KOH solutions. Raman spectra of aluminum Rim surfaces and data from KOH solution pH measurements strongly indicate that aluminum oxide cannot be the aluminum-passivating, layer, contrary to previously proposed models.