In high illumination conditions for photovoltaic converters, it is possible to stabilize the temperature of the photoactive region using a heatsink with high thermal conductivity, and by thinning the substrate that is a holder for semiconductor structure. However, the use of both methods together can lead to significant increase of the possible fragility of the converter. This work is devoted to the searching of balance between brittleness and overheating of GaAs/Ge solar cells installed on a copper heatsink with ceramic intermedia. Such composite heatsink, on the one hand, reduces mechanical stresses in the semiconductor, but, on the other hand, makes better the heat removal mode.