The goal of this research work is to develop an understanding as well as modelling thermal effects in Si based nano-scale devices using a multiscale simulator tool. This tool has been developed within the research group at Arizona State University led by Professor Dr. Dragica Vasileska. Another research group, headed by Professor Dr. Thornton, also at Arizona State University, provided support with software tools, by not only laying out the physical experimental device, but also provided experimental data to verify the correctness and accuracy of the developed simulation tool. The tool consists of three separate but conjoined modules at different scales of representation. 1) A particle based, ensemble Monte Carlo (MC) simulation tool, which, in the long-time (electronic motion) limit, solves the Boltzmann transport equation (BTE) for electrons, coupled with an iterative solution to a two-dimensional (2D) Poisson’s equation, at the base device level. 2) Another device level thermal modeling tool which solves the energy balance equations accounting for carrier-phonon and phonon-phonon interactions and is integrated with the MC tool. 3) Lastly, a commercial technology computer aided design (TCAD) software, Silvaco is employed to incorporate the results from the above two tools to a circuit level, common-source dual-transistor circuit, where one of the devices acts a heater and the other as a sensor, to study the impacts of thermal heating. The results from this tool are fed back to the previous device level tools to iterate on, until a stable, unified electro-thermal equilibrium/result is obtained. This coupled electro-thermal approach was originally developed for an individual n-channel MOSFET (NMOS) device by Prof. Katerina Raleva and was extended to allow for multiple devices in tandem, thereby providing a platform for better and more accurate modeling of device behavior, analyzing circuit performance, and understanding thermal effects. Simulating this dual device circuit and analyzing the extracted voltage transfer and output characteristics verifies the efficacy of this methodology as the results obtained from this multi-scale, electro-thermal simulator tool, are found to be in good general agreement with the experimental data.