A laser diode assembly contains a plurality of laser diode chips packaged closely in a row. Each laser diode chip is bonded on both P-side and N-side to first and second sub-mounts. The sub-mounts are then attached to a cooling carrier, with both bonding surfaces perpendicular to the top surface of the carrier. The direction of laser radiation is parallel to the carrier top surface, and the distance between the top of the active area of the laser diode chip and the carrier is preferably in a range of half a pitch between individual laser sources packaged in a row or preferably in a range of 0.2 mm to 1 mm to allow efficient cooling for high power operation. The sub-mounts may be electrically conductive, or they may be of insulating material at least partially covered with a conducting layer. A laser diode chip is bonded uniquely to a set of sub-mounts or may share a sub-mount with another laser diode chip.