Rugged, thin (<4 mil thick) GaAs-on-germanium 4 cm*4 cm solar cells with an AM0 conversion efficiency of up to 16.9% have been demonstrated. A processing technique suitable for high-volume production of large-area, thin cells has been established. The thinning technique developed here can also be used in the fabrication of high-efficiency lightweight GaAs/Ge and AlGaAs/Ge monolithic tandem cells.<<ETX>>