Novel ultra low-leakage ESD power clamp designs for wireless sensor applications are proposed and implemented in 0.18μm CMOS. Using new biasing structures to limit both subthreshold leakage and GIDL, the proposed designs consume as little as 43pW at 25 C and 119nW at 125 C with 4500V HBM level and 400V MM level protection, marking an 18-139× leakage reduction over conventional ESD clamps.