Transistors and their fabrication into very large scale integrated (VLSI) circuits are the invention that has made modern computing possible. Since its inception, integrated circuits have been advancing rapidly from a few transistors on a small silicon die in the early 1960s to 4 millions of transistors integrated on to a single large silicon substrate. The dominant type of transistor used in today’s integrated circuits is the metal-oxide-semiconductor (MOS) type transistor. The rapid technological advances in integrated circuit (IC) technology accelerated during and after the 1980s, and one of the most influential factors for such a rapid advance is the technology scaling, that is, the reduction in MOS transistor feature sizes. The MOS feature size is typically measured by the MOS transistor channel length. The smaller the transistors, the more dense the integrated circuits in terms of the number of transistors packed on to a unit area of silicon substrate, and the faster the transistor can switch. Not only can we pack more transistors onto a unit silicon area, the chip size has also increase. As the transistor gets smaller and silicon chip size gets bigger, the transistor’s driving capability decreases and the interconnect parasitics (interconnect capacitance and resistance) increases. Consequently, the entire VLSI system has to be designed very carefully to meet the speed demands of the future. Common design issues include optimal gate design and transistor sizing, minimization of clock skew and proper timing budgeting, and realistic modeling of interconnect parasitics.