Defects and degradation of InGa(Al)As/GaAs DQW diode laser bars mounted on copper micro-channel heat sinks were investigated. The analytical techniques used are optical microscopy and scanning electron microscopy. The high-power diode lasers were investigatively accompanied through the different phases of their setup process (i.e. mounting, characterization and burn-in). After the setup a long-term lifetest was performed. Changes in surface morphology in the facet area as well as changes in the threshold current, slope efficiency and emission spectrum are observed. Due to the degradation the threshold current increases and the slope efficiency decreases while the emission wavelengths are shifted to higher values showing a broadening of the spectrum. Formation of micro-cracks and alocations of crystalline areas within the facet area are observed. The influence of degradation an performance and life time of the high-power diode laser bars is discussed.