Power gating has been widely adopted in multicore designs. The design of fast and reliable power mode transition for per-core power gating remains a challenging problem. This paper studies the design methodology for fast power gating wake-up with guaranteed power integrity. Two novel techniques, namely current shaping and multi-thread activation are proposed. Models and physical implementation of both techniques are analyzed. Experimental results demonstrated 1.5 to 11 times wake-up time speedup with no penalty on area or power consumption by using the proposed techniques.