For application in space environments, the effect of 1-MeV electron irradiation on wafer-bonded GaInP/GaAs//InGaAsP/InGaAs four-junction solar cell grown by all solid state molecular beam epitaxy was studied. After exposure to 1-MeV electron irradiation at 1 x 15 e/cm(2), an end of life remaining factor of approximately 85% was obtained. The wafer bonding interface was studied by spectral response and transmission electron microscopy. 1-MeV electron irradiation was conducted on the individual InGaAsP and InGaAs single junction cell, respectively. The degradation of the four -junction cell was mainly due to damage on the InGaAsP and InGaAs subcells rather than the bonding interface.