A method for manufacturing a silicon interposer, includes a step of forming a protection film on a surface, on which an element portion is formed, of a silicon wafer, a step of forming open holes according to planar arrangements of through holes which pass through the silicon wafer in a thickness direction, a step of forming the through holes by etching the silicon wafer using the protection film as a mask, a step of forming an oxide film on inner wall surfaces of the through holes by a thermal oxidation, a step of forming a contact hole, which is in communication with the element portion, in the protection film, and a step of forming wirings on both surfaces of the silicon wafer. In the step of forming the wirings, one of the wirings is formed to be connected electrically to the element portion via a contact portion formed in the contact hole.