A wiring substrate includes a semiconductor substrate, an insulator and a plurality of columnar conductors. The insulator is made of an insulating material filled in a groove or hole provided in the semiconductor substrate. The plurality of columnar conductors are filled in grooves or holes provided in the insulator. The grooves or holes are arranged at a narrow pitch in a plane of the insulator. The insulating material has a Si—O bond obtained by reacting Si particles with an organic Si compound.