We are developing CAD tools, models and methodologies for electronics design for circuit operation in extreme environments with focus on very low temperatures (<20K). These new tools and methodologies will give rise to circuit designs that minimize the requirements for external heat sources that are currently often necessary for operation of low-temperature electronics. Such technology would 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 unique circuits and simulation tools that are derived from novel physics-based modeling techniques and verified by experiment. Temperature-stable designs and design methods will be provided as well. 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.