A semiconductor package may include first and second substrates, which are vertically stacked, a semiconductor device layer on a bottom surface of the second substrate to face a top surface of the first substrate, upper chip pads and an upper dummy pad on the top surface of the first substrate, penetration electrodes, which each penetrate the first substrate and are connected to separate, respective upper chip pads, lower chip pads on a bottom surface of the semiconductor device layer and electrically connected to separate, respective upper chip pads, and a lower dummy pad on the bottom surface of the semiconductor device layer and electrically isolated from the upper dummy pad. A distance between the upper and lower dummy pads in a horizontal direction that is parallel to the first substrate may be smaller than a diameter of the lower dummy pad.