A cooler for diode-laser bars comprises a machined base including a water-input plenum and a water-output plenum, and a top plate on which the diode-laser bars can be mounted. A stack of three etched plates is provided between the base and first plate. The stack of etched plates is configured to provide a five longitudinally spaced-apart rows of eight laterally spaced-apart cooling-channels connected to the water-input and water-output plenums. Water flows in the cooling-channels and in thermal contact with the first plate.