Simultaneous multithreading (SMT) as a processor design to achieve higher levels of system and application throughput is a well-accepted and deployed technique in most desktop and server processors. We study the power implications of varying SMT levels i.e., thread counts per core for various multi-threaded applications on a real SMT multicore platform, and introduce a novel software mechanism of changing SMT level of a core to tune platform power. Power-shifting policies by varying per core SMT levels for performance benefits within a power cap are introduced. Projected power savings (of 15%) for a streaming parallel benchmark can be attained using SMT-level power shifting mechanisms. © 2002-2011 IEEE.