In this paper, we propose a newly developed subthreshold slope (ideality factor) model, whose parameters are solely determined from the threshold voltage data. We succeed to express the ideality factor in terms of the threshold voltage parameters obtained from the body and DIBL effects, which can take care of its dependence on the process data such as channel length, oxide thickness, substrate doping profile, and junction depth in a parametric way. We prove the validity of our model bg comparing ours with the simulation and measurement results from nMOSFET devices with various oxide thickness, channel length, and doping profile.