Three-dimensional integration provides a new way of performance growth for microprocessor architectures. While a recent studies report promising performance improvement numbers, majority of the processor stacking options are thermally-limited. Elevated stack temperatures have significant effect on the overall energy efficiency and reliability of the processor; they also limit the potential peak performance improvement from the 3D implementation. Thermal characteristics of 3D stacks differ from 2D processors in various ways including: the nature of heat dissipation throughout the stack, thermal conductivity of the 3D structures such as micro-C4 layers, and hotspot interactions among layers. The intensity of the corresponding thermal problems is highly dependent on the 3D technology, processor and stack parameters. In this study we focus on spatial and temporal thermal characteristics of 3D multicore architectures using high-fidelity technology and processor models. Our experimental results highlight the need for integrating detailed thermal models in the design flow, starting with the early design stages. In addition, the reduced time constants and elevated on-chip temperatures indicate faster response time requirements for dynamic thermal management in processor stacking options. © 2012 ACM.