A method of forming through silicon vias (TSVs) uses a low-k dielectric material as a via insulating layer to thereby improve step coverage and minimize resistive capacitive (RC) delay. To this end, the method includes forming a primary via hole in a semiconductor substrate, depositing low-k dielectric material in the primary via hole, forming a secondary via hole by etching the low-k dielectric in the primary via hole, in such a manner that a via insulating layer and an inter metal dielectric layer of the low-k dielectric layer are simultaneously formed. The via insulating layer is formed of the low-k dielectric material on sidewalls and a bottom surface of the substrate which delimit the primary via hole and the inter metal dielectric layer is formed on an upper surface of the substrate. Then a metal layer is formed on the substrate including in the secondary via hole, and the metal layer is selectively removed from an upper surface of the semiconductor substrate.