Flexible high-efficiency III-V multijunction solar cells are being developed for use in unmanned Aerial Vehicles (UAVs), wearable devices and space applications. The solar cell epitaxial layers are grown on GaAs substrate by metalorganic chemical vapor deposition (MOCVD) and then are transferred to flexible substrates by cold-bonding and epitaxial lift-off process (ELO). Through the design of ELO apparatus and a large number of experiments on the optimal parameter, GaAs solar cell structure can be effectively separated from 4-inch GaAs wafer without defects and degradation in performance. Recently, 30 cm2 large area flexible GaInP/GaAs/InGaAs 3-junciton solar cells on 50 μm polyimide film achieved a 1-sun, AM0 conversion efficiency of 31.5% with an open-circuit-voltage of 3.01 V, a short-circuit current-density of 16.8 mA/cm2, and a fill factor of 0.845. By using the very light PI substrate, the unit weight of the solar cell is only 168.5 g/m2 and the specific power is up to 2 530 W/kg.