Abstract: A photoresist stripping solution is prepared by adding hydrogen peroxide to concentrated sulphuric acid under controlled temperature conditions, preferably at below 20.degree. C. The concentration of the sulphuric acid in the solution is preferably maintained at at least 80% wt to maximize the concentration of the active stripping species permonosulphuric acid. Stripping solutions having extended storage life have a content of soluble tim compound preferably sodium stannate and preferalby also a phosphonate sequestrant which shows a synergism with the tin compound. Such extended life solutions also preferably have a low content of transition metals and of particles. The stripping solution may be utilized at ambient temperature.

Abstract: A storable semiconductor cleaning solution consists essentially of sulphuric acid at a concentration of from 30% to 70% and hydrogen peroxide at a concentration of from 1% to 20% preferably also containing a pentavalent phosphorus sequestrant and tin ions. The solution is produced by diluting concentrated sulphuric acid, aging the diluted acid until it reaches a temperature below 30.degree. C. and introducing the hydrogen peroxide, preferably having a concentration of at least 70% by weight, into the aged acid and equilibrating the resulting solution. The cleaning solutions can be stored for an extended period at ambient temperature and can be used to clean semiconductors, and with suitable precautions aluminized semiconductors, at temperatures below 100.degree. C.