PURPOSE: To obtain spherical quartz glass powder which is high purity and has projecting parts of a network pattern on the surface with high yield, by dispersing the partial condensate of water-insoluble silicon alkoxide into water and calcining the pptd. silica gel.

CONSTITUTION: Sol of partial partial condensate of silicon alkoxide is formed by hydrolyzing silicon alkoxide with water of 0.7W1.3mol. times for 1mol. of silicon alkoxide under the existence of acid and alcohol. Then the partial condensate of water-insoluble silicon alkoxide is formed by removing alcohol from this sol. Thereafter the ppt. of silica gel is formed under the existence of a gelling agent by dispersing the partial condensate of water-insoluble silicon alkoxide into water and the aimed quartz glass powder is obtained by calcining the pptd. silica gel. The composition obtained by mixing this quartz glass powder with resin is large in the contact area of the powder and resin and is excellent in fluidity and is free from impurities and therefore is especially suitable for seal of a semi-conductor device.