This article presents a physics-based hydrodynamic modeling approach for antenna-coupled 65 nm Si MOSFETS at terahertz frequencies. The model is based on 1-D hydrodynamic transport equations describing continuity and momentum balance and accounts for mixing processes of the charge-carrier density waves in the FET channel. Numerical evaluation of the hydrodynamic model performed in Keysight’s ADS simulation environment is compared to TSMC’s RF modeling tool for four different devices for fundamental device characteristics, and the results of both modeling techniques are compared to measurements. The TSMC RF model proves to be useful well beyond its intended 5G applications to about 1.2 THz when plasmonic mixing terms are likely to dominate device response.