A new effect, called random trap fluctuation(RTF), is proposed to study the impact of hot carrier stress on the device variability. It was found that not only the popular random dopant fluctuation (RDF), but also the traps, caused by the HC stress or FN-stress, induce the Vth variation. After the FN stress, it was found that Vth variation is worse in pMOSFETs due to stress-induced interface traps. While, under the HC stress, different V th variations were found for nMOSFETs and pMOSFETs. The V th variation is enhanced in pMOSFETs due to RTF and reduced in nMOSFET as a result of the Trap Blocking Effect (TBE). RTF in pMOSFET might be the dominant factor of CMOS reliability for future generations.