This paper studies hot spot and thermal coupling problems in future multicore architectures as CMOS technology scales from 65 nm feature size to 15 nm. We demonstrate that the thermal coupling between neighboring cores will dramatically increase as the technology scales to smaller feature sizes. The simulation studies were based on solving the heat equation using the analytical Green's function method. Our simulations indicate that the thermal coupling in the 15 nm feature size just after 100 ms of operation will increase from 20 % to 42 % and in the steady state might reach even 65 %. This finding uncovers a major challenge for the design of future multi-core architectures as the technology keeps scaling down. This will require a holistic approach to the design of future multi-core architectures encompassing low power computing, thermal management technologies and workload distribution.