Dynamic Electroluminescence Imaging (DEI) is a technique used to observe semiconductor devices as they operate. Much like a traditional oscilloscope, the technique delivers waveform information that is useful for assessing the operation of the circuits that comprise a device. It can be thought of as a non-contact “optical oscilloscope probe”. The technique has two major advantages over traditional electrical oscilloscope probing. The technique is noninvasive and has a theoretical bandwidth approaching 100 GHz. This means that very fast signals can be observed without unduly loading or otherwise interfering with the circuitry under test. Moreover, the characterization of signals at individual nodes along a signal path allows problems that arise from intervening interconnects and transmission lines to be identified. This paper will show several examples of the radio frequency (RF) measurement capabilities of this technique that have been demonstrated in our laboratory.