A semiconductor interposer is provided, which includes: a substrate body having a surface defined with an inner area and a peripheral area around the inner area; a plurality of conductive posts embedded in the substrate body and each having one end exposed from the surface of the substrate body; a passivation layer formed on the surface of the substrate body and having a peripheral portion formed in the peripheral area, a plurality of ring-shaped portions formed around peripheries of the exposed ends of the conductive posts in the inner area and a plurality of strip-shaped portions formed between the ring-shaped portions for connecting the ring-shaped portions; and a UBM layer formed on the exposed end of each of the conductive posts and extending on the ring-shaped portion around the periphery of the exposed end of the conductive post, thereby effectively reducing stresses to prevent warping of the semiconductor interposer.