The conditions and reaction mechanism of W/Ni/Si80Ge20hot‐press bonding have been studied. It was found that a Ni/Si80Ge20bond can be formed using low pressure, 19.6 MPa, in the temperature range between 780 and 900 °C in a short time. The kinetics follows a parabolic pattern, suggesting it is a diffusion‐controlled process. The activation energy is 2.7 eV and the parabolic rate constant is given byKP= 4.0 × 1014 exp(−3.2×104/T) (&mgr;m2/min). The bonding interface has a multilayered structure. A phenomenological mechanism of the bonding formation has been proposed based on scanning electron microscopy observations and energy dispersive spectroscopy. The cracking problem due to thermal stress is discussed based on Oxx’s equation. It was found that bonds free from cracks in the Si80Ge20alloy are formed when the Ni consumption (as measured by the thickness of the nickel layer) is sufficiently small (<40–45 &mgr;m) and the post‐hot‐press cooling is slow. On the other hand, tungsten and nickel react during hot pressing at higher temperature, forming WNi4. As an interlayer, nickel can join the tungsten sheet and the Si80Ge20together. It has been also demonstrated that a thin nickel layer formed by vapor deposition on a tungsten sheet may be used as the interlayer in place of nickel sheet.