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Random telegraph noise (RTN) and negative bias temperature (NBT) stress-induced threshold voltage (Vt) fluctuations in high-κ gate dielectric and metal-gate pMOSFETs are investigated. We measured RTN amplitude distributions before and after NBT stress. RTN in poststressed devices exhibits a broader amplitude distribution than the prestress one. In addition, we trace a single trapped charge-induced ΔVt in NBT stress and find that the average ΔVt is significantly larger than a ΔVt caused by RTN. A 3-D atomistic simulation is performed to compare a single-charge-induced ΔVt by RTN and NBTI. In our simulation, the probability distribution of a NBT trapped charge in the channel is calculated from the reaction-diffusion model. Our simulation confirms that the NBT-induced ΔVt indeed has a larger distribution tail than RTN due to a current-path percolation effect.