Au-Sn is an excellent material with superior attributes and is the solder of choice, with no obvious alternatives, in many microelectronic applications. Recently, this alloy has been chosen as a potential candidate for bonding in wafer level hermetic packaging at high temperature using WN as diffusion barrier. In this application, good wetting of WN by the liquid Au-Sn alloy is a key factor for the bonding process. To this end, wetting of W (x) N (covered or not by a gold layer) by Au-Sn20 alloy was studied at 380 A degrees C under high vacuum. Excellent wetting was observed when W (x) N was protected from oxidation by a thin Au layer. The spreading process was found to be followed by a complete dissolution of a protection layer and slight receding of the triple line. Some preliminary bonding tests using Au-Sn alloy were also performed.