A semiconductor device package ready for assembly includes: a semiconductor substrate; a first under-bump-metallurgy (UBM) layer disposed on the semiconductor substrate; a first conductive pillar disposed on the first UBM layer; and a second conductive pillar disposed on the first conductive pillar. A material of the first conductive pillar is different from a material of the second conductive pillar, and the material of the second conductive pillar includes an antioxidant.