The present analysis proposes an analytical model of gate-all-around /surrounding gate (GAA/SG) MOSFETs for centroid including quantum mechanical (QM) effects. To obtain the QM effects of SGT, the coupled Poisson and Schrodinger equations are solved using variational approach. This model is developed to provide an analytical expression for inversion charge distribution function(ICDF). The obtained ICDF is used to calculate the inversion charge centroid. The accuracy of the model is verified by comparing the data obtained by Simulations.