In this paper, a quantitative study of the corner effect and of the local volume inversion on gate-all-around MOSFETs based on numerical simulations has been carried out; different angles and doping levels are compared, in order to understand the impact of the corner regions on the total current. A method for the extraction of the threshold voltage and of the subthreshold slope of the corner region has been proposed, and the resulting values have been analyzed in order to understand their effects on the device characteristics.