We are developing CAD tools, models and methodologies for electronics design for circuit operation in extreme environments with a focus on very low temperature and radiation effects. These new tools and methodologies will help enable NASA to design next generation electronics. Such capabilities will significantly improve reliability, performance and lifetime of electronics that are used for space applications, including satellites and space travel. This will be achieved through the development of novel physics-based modeling techniques and verified by experiment. The new cryogenic design tools will greatly reduce the chances of error during actual circuit implementation, and thus reduce the number of design cycles, thereby substantially decreasing fabrication times and expenses. Models and CAD tools are relatively inexpensive as compared to fabrication costs; thus the results of this project should provide a very large return on investment.