Lightweight constructions are currently of high interest for several industrial applications, like shipbuilding. Thus, CO2 emissions can be reduced and higher driving speed can be achieved. For this purpose, hybrid joints of steel and aluminum parts are in great demand. However, welding of this material combination is characterized by low weldability. In particular, different physical properties and formation of intermetallic phases may lead to cracks. In these investigations, high-power laser welding processes are developed for thick dissimilar lap joints of steel and aluminum alloys. In this context, influence of welding parameters on weld seam quality is determined by using visual inspection, metallographic analyzes and tensile shear testing. Using suitable parameters, comparatively high weld seam quality and seam strength can be achieved. As the weld seam quality depends strongly on the mixture ratio, penetration depth must be controlled. Thus, an in-process control of the penetration depth is successfully developed and validated.