As shown in this project the thought of using digital circuits for more than representing two values is almost as old as the semiconductor. In this thesis some of the history of multiple-valued circuits is described. One of the main aims of representing more than two values in a system is to save energy. Severalmethods of power saving are mentioned, such as reduction of Vdd, reduction in swing of signals and power down to mention a few. The main scope as the title implies is on semi-floating-gate circuits. Also a few circuits are presented to explain the technology utilized in the practical part of the project. Finally the use of multiple-valued semi-floating-gate circuits as parallel and serial multipliers is presented.