Wafers including a diamond layer and a semiconductor layer having III-Nitride compounds and methods for fabricating the wafers are provided. A nucleation layer, at least one semiconductor layer having III-Nitride compound and a protection layer are formed on a silicon substrate. Then, a silicon carrier wafer is glass bonded to the protection layer. Subsequently the silicon substrate, nucleation layer and a portion of the semiconductor layer are removed. Then, an intermediate layer, a seed layer and a diamond layer are sequentially deposited on the III-Nitride layer. Next, a support wafer that includes a GaN layer (or a silicon layer covered by a protection layer) is deposited on the diamond layer. Then, the silicon carrier wafer and the protection layer are removed.