Despite the rapid development in semiconductor-based devices, there exist fundamental materials and physics issues that limit the reliability and performance of optoelectronic and electronic devices. This book examines the latest technical advancements and emerging trends in semiconductor materials and devices. The Gallium Nitride Electronic Devices chapter offers an overview of the state-of-the-art in high electron mobility transistor (HEMT) devices with interesting work on circumventing the current performance limiters in this device structure. Nano-Engineered Devices provides a snapshot of the current understanding in modifying the nanoscale specific properties of quantum dot and quantum well devices. The Performance of Semiconductor Devices chapter surveys advancements in several fields including terahertz ellipsometry, high-power multi-emitter laser bars, and thin-film transistors. Advanced Materials and Devices, highlights designs in ultrathin high-kappa gate dielectrics for CMOS and related devices and also reports on the implementation of III-V materials as a replacement for the silicon channel in future CMOS technology.