Abstract: We have developed a multiscale method to model emerging electronic devices. It features a combination of first-principles calculation, semi-classical semiconductor device simulation, compact model generation and circuit simulation. We have applied the method to model a new type of transistors and their circuits: junctionless field-effect transistor. The transfer characteristics of junctionless field-effect transistors are simulated by a recently developed quantum mechanical/electromag- netics method, and good agreement is obtained compared to experiment. A compact model of junctionless transistors is then generated for subsequent circuit simulation. We demonstrate a multiscale modeling framework for quantum mechanical effects in nano-scale devices for next generation electronic design automation.