In this paper we have studied the effect of process variations on unity gain cut- off frequency (ft) in conventional and junctionless gate-all-around (GAA) transistors using TCAD simulations. Three different geometrical parameters, channel doping, source/drain doping (for conventional GAA), wire doping (for junctionless GAA) and gate electrode work function are studied for their sensitivity on ft. For conventional GAA, ft is more sensitive to gate length and source/drain doping and less sensitive to gate oxide thickness, ovality and channel doping and least sensitive to gate work function variations. For junctionless GAA, ft is more sensitive to gate length and gate work function variations and less sensitive to gate oxide thickness, ovality, wire doping. The non-quasi static (NQS) delay is extracted for the most sensitive parameters. The trend of NQS delay is just the reverse trend of ft. © School of Engineering, Taylor’s University.