Thermal management of LED is currently an important issue because the increase of junction temperature degrades LED's performance and reliability. Replace that substrate to high thermal conductivity substrate can improved this problem. Diamond has the highest thermal conductivity (~2000W/mK) in all material but is hard to process and has low reactivity with other material. In this study, high-brightness ?-? light-emitting diodes on Si/diamond composite substrate can be fabricate by filled diamond particle into the blind-hole of the silicon substrate, wafer-bonding and lift-off process. In order to confirm that diamond particle provided a direct thermal path for heat dissipation, a simple sandwich structure was also been done.