Wafer bonding has become the mainstream technology for developing GaN-on-Diamond devices. Room temperature bonding technology can avoid lattice mismatch and differences in thermal expansion coefficients caused by high temperature growth process, and there is no need to consider the low thermal conductivity of the nucleation layer. The use of diamond with high thermal conductivity as a bonding material can maximize the heat dissipation capacity. Therefore, the work aims to study the bonding technology between polycrystalline diamond and GaN with Ti/Ag intermediate layer at room temperature.