Many applications of vertical-external-cavity surface-emitting lasers (VECSELs) , such as intra-cavity frequency mixing rely on the high-power characteristics of the devices. Generally, overheating limits any lasers performance and, thus, efficient cooling concepts are crucial for the high-power output . Here, we experimentally investigate the thermal properties of a high-power device, focusing on the generation, distribution and removal of excess heat under extreme pumping conditions. Different heat-spreading and heat-transfer approaches are analyzed. The performance of the device is optimized yielding a maximum emitted power beyond 70W from a single spot. Finally, the potential for power-scaling in VECSELs and its restrictions are examined. Details on the chip and the experimental setup are given in .