This thesis outlines the principles, device physics, and technological applications of electronics based on the ultra-wide bandgap semiconductor aluminum nitride. It discusses the basic principles of electrostatics and transport properties of polarization-induced two-dimensional electron and hole channels in semiconductor heterostructures based on aluminum nitride. It explains the discovery of high-density two-dimensional hole gases in undoped heterojunctions, and shows how these high conductivity n- and p-type channels are used for high performance nFETs and pFETs, along with wide bandgap RF, mm-wave, and CMOS applications. The thesis goes on to discuss how the several material advantages of aluminum nitride, such as its high thermal conductivity and piezoelectric coefficient, enable not just high performance of transistors, but also monolithic integration of passive elements such as high frequency filters, enabling a new form factor for integrated RF electronics.