A method of manufacturing an interposer substrate, including providing a carrier having a first circuit layer formed thereon, forming a plurality of conductive pillars on the first circuit layer, forming a first insulating layer on the carrier, with the conductive pillars being exposed from the first insulating layer, forming, on the conductive pillars a second circuit layer that is electrically connected to the conductive pillars, forming a second insulating layer on the second surface of the first insulating layer and the second circuit layer, exposing a portion of a surface of the second circuit layer from the second insulating layer, and removing the carrier. The invention further provides the interposer substrate as described above.