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In this study, we have fabricated the high-power GaNbased vertical light-emitting diodes (VLEDs) by exploiting a thermally stable nano-scaled Ni-Ag-Ni-Au mirror. After being treated at 600 C for 1 min in air ambient, the nano-scaled Ni-Ag-Ni-Au (5/2000/1000/2000 Å) mirror shows the specific contact resistance of cm and its reflectivity has increased from 89.5% to 93.0%. The increment in the reflectivity is due to the diffusion of Ni contact layer into Ag layer. Moreover, the reflectivity of the mirror has hardly deteriorated even after the wafer was thermally bonded with graphite substrate at 320 C for 5 min, meaning that the proposed mirror is thermally reliable. The light output power of the nano-scaled VLED (Chip size: 1 1 mm ) with thermal treatment at 600 C for 1 min is enhanced by 8% as compared to one without thermal treatment at an injection current of 350 mA. To our knowledge, our nano-scaled mirror has the highest reflectivity among other Ag-based multilayered reflectors, and thus it is a promising candidate for high-performance VLED. Index Terms-GaN, light-emitting diodes (LEDs), light output power, thermally stable mirror, wafer bonding.

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