Aqueous dispersion containing a silicon-aluminum mixed oxide powder, the powder containing 0.1 to 99.9 wt. % Al.sub.2O.sub.3 and Si--O--Al-bonds. The dispersion can be produced using dispersing and/or grinding devices which a achieve an energy input of at least 200 KJ/m.sup.3. The dispersion can be used for the chemical-mechanical polishing of semiconductor substrates.