Injection moulding is one of the most productive plastic forming processes. Product development and the reduction of production time require new solutions in tooling design and manufacturing. Direct metal laser sintering (DMLS) allows moulds to be built with special cooling systems, which offer curved cooling lines that can follow the geometry of the part (conformal cooling). One disadvantage of DMLS, its high cost, can be dramatically reduced with the building of hybrid structures. With conventional tool steels as the base plate and only the special geometry of the part sintered on the top, the final geometry can be manufactured after sintering by conventional process technologies. We produced hybrid structures by direct metal laser sintering maraging steel (MS1) powder onto the surface of commercial mould steels and studied the effect of different heat treatments on porosity, tribological behaviour and the microstructure. The transition zone was also characterized.