Thermal management for 3D ICs is becoming a crucial challenge. The liquid cooling architecture using built-in micro-channels is effective for cooling very high-performance 3D systems with advanced microprocessors, but it is very expensive because additional fabrication process and high reliability to maintain a quality are required. 3D ICs are not applied only for such advanced high-performance systems. In this paper, we propose new architectures to solve thermal problems of middle-power 3D systems with power dissipation of several ten watts. By using the sidewalls (which are made by thermal cap, bridge, or poles) surrounding stacked chips, thermal inter-chip plates, and thermal bottom plate, the architectures can secure heat conduction paths to the heat sink that removes most of the heat generated in the devices. The experimental results obtained by using a 3D thermal solver demonstrate that the proposed architectures having some variations can reduce the maximum temperature in a 3D IC significantly. Especially, the proposed basic structure achieved the temperature reducing effect over 25 °C compared with the conventional structure with heat sink only.