Statistical process variations are a critical issue for circuit design strategies to ensure high yield in sub- 100nm technologies. In this work we investigate the variability of flip flop race immunity in 130nm and 90nm low power CMOS technologies. An on-chip measurement technique with resolution of ˜1ps is used to characterize hold time violations of flip flops in short logic paths, which are generated by clock-edge uncertainties in synchronous designs. Statistical die-to die variations of hold time violations are measured various register-to-register configurations and show overall 3σ die-to-die standard deviations of 12–16% Mathematical methods to separate the measured variability between systematic and random variability are discussed, and the results presented. They show that while systematic variability is the major issue in 130nm, it is significantly decreased in 90nm technology due to better process control. Another important point is that the race immunity decreases about 30% in 90nm, showing that smaller clock skews can lead to violations in 90nm.