Power dissipation in LSI chips for PC notebooks, network servers, and inverters has grown so rapidly that the density of heat generation may exceed heat fluxes to boil water in steam boilers and LWEs. In addition, such electronic devices are undergoing downsizing. These trends require the advent of novel thermal management techniques using micro thermal devices to keep the chips at a temperature below the permissible limit. The technological strategy coping with such trends consists of the following two stages, lb reduce the cooling load, in addition to the development of low power LSIs, micro converters of the power dissipation to electricity should be developed. Next, to transfer the remaining heat effectively to the ambient, micro thermal devices should be developed. In the present paper, focusing on the application of micro-channel heat transfer and micro groove evaporation to the thermal management of electronic devices, the channel or groove size desired for high-performance heat-spreading plates and compact heat sinks is discussed from the viewpoint of optimization. In particular, the present paper introduces a high-performance heat-spreading plate containing a new heat pipe, micro-channel heat sinks for PC notebooks, and micro-groove heat sinks for network servers.