A method for forming a semiconductor package structure is provided. The method for forming a semiconductor package structure includes providing a substrate, wherein the substrate has a front side and a back side, forming a first guard ring doped region and a second guard ring doped region in the substrate, wherein the first guard ring doped region and the second guard ring doped region have different conductive types, forming a trench through the substrate from a back side of the substrate, conformally forming an insulating layer lining the back side of the substrate, a bottom surface and sidewalls of the trench, removing a portion of the insulating layer on the back side of the substrate to form a through via, and forming a conductive material in the through via, wherein a through silicon via (TSV) interconnect structure is formed by the insulating layer and the conductive material.