© 2019 Author(s). A more realistic approach to evaluate the impact of polycrystalline metal gates on the MOSFET variability is presented. 2D experimental workfunction maps of a polycrystalline TiN layer were obtained by Kelvin Probe Force Microscopy with a nanometer resolution. These data were the input of a device simulator, which allowed us to evaluate the effect of the workfunction fluctuations on MOSFET performance variability. We have demonstrated that in the modelling of TiN workfunction variability not only the different workfunctions of the grains but also the grain boundaries should be included.