Time correlated single photon electroluminescence maps have been recorded on operating semiconductor devices with a spatial resolution approaching 1 mu m and a time resolution of 50 ps. The technique is noninvasive and observes signal wave forms optically, directly at the device. Spectral measurements in the near infrared and visible were also performed. Two examples of the application of this technique to semiconductor devices are presented. An AlGaAs/GaAs heterojunction bipolar transistor typical of high speed bipolar devices used in rf circuitry, and an AlGaN/GaN heterostructure field-effect transistor as an example of the application of optical techniques in characterizing the emerging technology. (c) 2006 American Vacuum Society.