The effect of particle radiation in multi quantum well (MQW) multi-junction InGaP/MQW-InGaAs/Ge solar cells was studied. For comparison purposes, and to identify the origin of the degradation, the same study was performed in the correspondent iso-type cells. Results show that under 1MeV electron irradiation the MQW-middle junction dictates the degradation of the triple junction cell. Alternative, more radiation hard, designs are presented.