In this paper, self-consistent three-dimensional (3D) device simulations for exact analysis of thermal transport in FinFETs are performed. We analyze the temperature rise in FinFET devices with the variation in the number of fins (Nfin), shape of fins and fin pitch (Fpitch). We investigate that the thermal resistance Rth has nonlinear dependency on Nfin and Fpitch. We formulate a model for thermal resistance behavior correctly with Nfin and Fpitch variation. The proposed formulation is implemented in industry standard Berkeley short-channel independent gate FET model for common multi-gate transistors (BSIM-CMG) and validated with both experimental data and TCAD simulations.