Transistors are the most important active structure of any semiconductor component. Performance characteristics of such devices within the specifications are key to ensuring proper functionality and long-term reliability of the product. In this article, a summary of the semiconductor technology from design to manufacturing and the characterization methods are discussed. The focus is on two prominent MOS structures: planar MOS device and FinFET device. The article covers the device parameters and device properties that determine the design criteria and the device tuning procedures. The discussion includes the effects of drain induced barrier lowering, velocity saturation, hot carrier degradation, and short channel on these devices.