To obtain the subject slurry having a stable polishing characteristic in the vicinity of neutral condition and high selectivity between an insulation film and an electroconductive film, and capable of accomplishing control of dishing by including polishing particles comprising mixed crystal particles composed of silica and alumina.

This slurry is obtained by including polishing particles comprising mixed crystal particles composed of (A) silica and (B) alumina. In this slurry, the mixed crystal ratio of the component B to the component A is pref. 1 to 9, and this slurry is pref. at pH 4 to 9. Further, it is desirable that' ammonium peroxodisulfate or hydrogen peroxide is used in this slurry as an oxidizing agent because there is no need of changing the pH of the slurry within the range from 4 to 9. This slurry, as necessary, may include an oxidation retarder, polishing particles, dispersant, an organic acid or the like aiming at improvement of holding the particles on a polishing pad.