In this paper, we present a technique for device temperature measurement using spontaneous near infrared (NIR) emission from an Integrated Circuit (IC). By leveraging modeling and data analysis, time-integrated emission measurements are used to estimate the temperature increase due to switching activity inside the channel of CMOS transistors. The non-invasive nature of the technique allows one to reliably monitor the temperature of any device on-chip without the need for circuit modifications or dedicated on-chip sensors and with a higher spatial resolution than thermal cameras. This method has important applications for modeling heat dissipation during early process development, localizing hot spots, calibrating on-chip sensors, etc. In this paper, temperature is estimated by fitting empirical emission data to an emission model that can be solved for device channel temperature.