Removal of heat from semiconductor at power densities of 1 W/mm2 and higher has traditionally been the arena of liquid cooled cold plates in combination with a thermal interface material (TIM) coupling the cold plates to the heat generating devices. In standard rigid liquid cooled cold plate applications, the TIM is responsible to both conduct heat and absorb both static and dynamic mechanical surface mismatches between the cold plate and the device. This dual mission generally constrains the thermal performance of the TIM. In some applications like high power device test, the materials allowed for the TIM are further constrained, resulting in difficulty obtaining desired thermal performance. This work describes an innovative approach to conducting heat while providing mechanical compliance, allowing higher performance from most TIM's and allowing a wider range of TIM's for a given required thermal performance. The development of this approach from a heat conducting compliant interposer, to an interposer with an integrated high performance heat sink, to the final very high performance heat sink which flows liquid coolant through the compliant interposer structure incorporating high heat transfer fins is described. The heat sink provides junction to water thermal resistances as low as 16 Cmm2/W (including the full semiconductor die resistance) while greatly reducing variability in thermal resistance across the device being cooled when compared with rigid heat sinks. The high thermal performance is accomplished at reasonable pressure drop through the use of multiple manifolding of short 55 mm width channels and fins. Both mechanical and thermal response data are presented in detail.