The substrate for a semiconductor package includes a substrate body having a first surface and a second surface opposite to the first surface. Connection pads are formed near an edge of the first surface. Signal lines having conductive vias and first, second, and third line parts are formed. The first line parts are formed on the first surface and are connected to the connection pads and the conductive vias, which pass through the substrate body. The second line parts are formed on the first surface and connect to the conductive vias. The third line parts are formed on the second surface and connect to the conductive vias. The second and third line parts are formed to have substantially the same length. The semiconductor package utilizes the above substrate for processing data at a high speed.