Abstract: A process for cleaning quartz and silicon surfaces by removing inorganic substances from said surfaces which comprises contacting the surface to be cleaned with a liquid at a temperature and for a period of time effective to remove said substances from the surface, said liquid comprising a solution in a solvent of at least one quaternary ammonium hydroxide characterized by the formula ##STR1## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are each independently alkyl groups containing from 1 to about 10 carbon atoms, aryl groups, or R.sub.1 and R.sub.2 are alkylene groups which together with the nitrogen atom may form an aromatic or non-aromatic heterocyclic ring provided that if the heterocyclic group contains a --C.dbd.N-- bond, R.sub.3 is the second bond.