Quantum effects are predominant in tri-gate MOSFETs, so a model should be developed. For the first time, this paper presents the analytical model for quantization effects of thin film silicon tri-gate MOSFETs by using variational approach. An analytical expression of the inversion charge distribution function(ICDF) or wave function for the tri-gate MOSFETs has been obtained. This obtained ICDF is used to calculate the important device parameters, such as the inversion charge centroid and inversion charge density. The results are validated against with the simulation data. For the first time, this paper presents the analytical model for quantization effects of thin film silicon tri-gate MOSFETs by using variational approach. An analytical expression of the inversion charge distribution function (ICDF) or wave function for the tri-gate MOSFETs has been obtained. This obtained ICDF is used to calculate the important device parameters, such as the inversion charge centroid and inversion charge density. data.