The actual mechanism involved in Au-Si wafer bonding is controversial. Usually a titanium or chromium layer is deposited in between the (oxidized) silicon substrate and the gold layer to ensure adhesion. The resulting bond of two such wafers after annealing is generally considered to be eutectic, however, the bond temperature required is higher than would be expected from the Au-Si eutectic temperature. Moreover, silicide grains are formed at the bonding interface. In this paper it is proposed that the actual bonding is initiated by the dissolution of the oxide layer by silicidation of the titanium adhesion/barrier layer. The subsequent direct Au-Si contact enables the formation of the euteetic phase. The silicidation is required to obtain the eutectic alloy with 19 at.% Si despite the Ti diffusion barrier. The bonding temperature required is, therefore, set by the silicidation process rather than by the eutectic phase. Several experiments have been designed to support this theory. AI-Si eutectic bonding has been investigated, as it is not complicated by an adhesion metal and experiments demonstrate reliable bonding close to its eutectic temperature. Moreover, a Ti/Au/Si/Au stack has been fabricated to be used as a eutectic solder, giving bonding at a temperature not affected by silicidation. Keywords Eutectic bonding Gold Silicide bonding Silicon Wafer bonding