Cold Source Field Effect Transistor (CSFET) enabled by source engineering is a promising candidate to achieve unique sub-60 mV/dec steep-slope switching. For the first time, we present an industry-standard multiscale TCAD framework for CSFET with proposed effective cold carrier distribution model, which captures the underlying physics of cold carrier injection efficiency, and carrier thermalization. The multiscale framework incorporates Non-Equilibrium Green’s Function (NEGF) simulations for validation. The effects of geometry configuration and source engineering are extensively investigated on a Si-based Double-Gate (DG) CSFET.