High-power microwave semi-conductor devices based on silicon and gallium arsenide are energetically inefficient, much of the power injected being dissipated thermally. Good heat-sinking of these devices is, therefore, essential and the physical properties of silver and gold suggest their application. The provision of electrodeposited silver and gold heat-sinks is discussed, concentrating particularly on the requirements for good device performance and efficient manufacture. Additionally, some possible influences on device reliability are considered.