Negative Capacitance (NC) obtained from the ferroelectric (FE) polarization switching is a widely adopted approach for the realization of low power, high-performance devices. In this paper, for the first time, we have developed a 3D quasi-analytical model for the surface potential and drain current of the Trigate (TG) NC-FinFET using the superposition approach. Till date, only double gate uniformly doped NC-FinFET structures have been explored, which does not reveal the practicality of the device. Therefore, we perform an extensive device evaluation: 1) by solving the Poisson equation separately for the side gates (double gate) and the top gate to acquire a complete model for tri-gate FinFET using superposition principle; 2) to mimic the actual source/drain (S/D) doping, we included Gaussian doping in our proposed model; 3) with the incorporation of the laterally extended gate and S/D underlap. The model data are found in good agreement with the well-calibrated simulation data. We have taken the parabolic approximation method and appropriate boundary conditions to solve the Poisson equation.