Mechanical pressure exerts a noticeable effect on the reaction that takes place at the interfacial region of Si3N4/Ni-Cr-B/Si3N4 joints. In fact, the mechanical pressure affects the thickness of the reaction layer: for lower pressures, a large interfacial reaction layer and a profusion of cracks are observed, whereas, for higher pressures, the extent of the reaction layer is limited, and no cracks are detected. The results show that joint strength increases monotonically with applied pressure.