We found degraded output power due to discoloration of an abnormal epitaxial layer caused by supercooling of residual melt in liquid phase epitaxy (LPE) process of AlGaAs/GaAs heteroface solar cells developed to improve conversion efficiency of solar cells for satellites. We studied the discoloration mechanism and found effective methods for obtaning a good epitaxial layer. Using these results, we manufactured about 80,000 pieces of solar cells and employed them in the Japanese domestic Communication Satellite-3 (CS-3) launched by National Space Development Agency of Japan (NASDA). Five years after launch, these solar cells are still supplying the output power than predicted. This paper describes reliability improvements for the surface of epitaxial layer and successful results aftes 5 years of space operation.