Provided is a submount flip-chip bonded to a semiconductor laser diode chip with stepped first and second electrodes. The submount includes a substrate having first and second surfaces which are separated by a step height corresponding to a height difference between the first and second electrodes; first and second metal layers being formed to the same thickness on the first and second surfaces, respectively; and first and second solder layers being formed to the same thickness on the first and second metal layers, respectively, and being bonded to the first and second electrodes, respectively.