Abstract: A metal inter-diffusion bonding method for forming hermetically sealed wafer-level packaging for MEMS devices. A stack of a first metal is provided on a surface of both a first wafer and a second wafer, the first metal being susceptible to oxidation in air; providing a layer of a second metal, having a melting point lower than that of the first metal, on an upper surface of each stack of the first metal, the layer of second metal being sufficiently thick to inhibit oxidation of the upper surface of the first metal; bringing the layer of the second metal on the first wafer into contact with the layer of second metal on the second wafer to form a bond interface; and applying a bonding pressure to the first and second wafers at a bonding temperature lower than the melting point of the second metal to initiate a bond, the bonding pressure being sufficient to deform the layers of the second metal at the bond interface.