An interposer may include a first base, at least one first signal line in the first base, and at least one first ground line in the first base, wherein the ground line surrounds the at least one first signal line. The at least one first signal line and the at least one first ground line may be exposed through an upper surface of the first base. The at least one first signal line may be configured to conduct a test current through the first base. An interposer may also include a second base below the first base and may include a printed circuit board between the first base and the second base. A probe card may include a multilayer substrate having at least one contact needle, a coaxial board having at least one coaxial signal cable and the above described interposer between the multilayer substrate and the coaxial board.