Technology scaling has involved advances in the integration of radio frequency (RF) circuits that have allowed the development of high-performance communication systems. As the complexity of these systems-on-chip (SoCs) grows, their complexity and performances increase, and their debugging and testing becomes more difficult, mainly due to the limited observability of their RF nodes. Being able to observe the performances of individual blocks that constitute the transceiver chain is beneficial for the identification of faulty devices that would result in improved efficiency during production testing. At the same time, technology scaling has provoked the increase of technological parameter variation and more severe aging effects; furthermore, as the technology scales down, both time-zero variability (process variation) and time-dependent variability (aging) gain in importance as their effect on both digital and analog/RF circuitry becomes greater [Yid11,Garg13]. The availability of reliable internal RF power measurements promises to ease the pass–fail testing of transceivers and also may enable the use of active knobs embedded in self-healing schemes to enhance system performance and to correct electrical performance modifications due to process variation and aging [Ona12]. In conventional built-in self test (BIST) characterization strategies, power detectors are strategically placed at nodes of the circuit under characterization in order to measure the power of a test signal along the signal path. The paradigm is that electric power detectors have to be reliable and must operate at RF frequencies to be useful. Although small, the finite input impedance of RF detectors degrades the performance of the transceiver chain, especially if the auxiliary devices are placed at critical nodes such as the low-noise amplifier (LNA) input, mixer, and frequency synthesizer where additional parasitic capacitances cannot be tolerated [Bow13]. Evidently, the degradation becomes more critical as system performance and operating frequency increase. In this direction, a novel noninvasive test and characterization strategies suitable for RF SoCs employing DC and low-frequency noninvasive temperature measurements are described in this chapter.