Fluorescent microthermal imaging (FMI) is used to measure the temperature at the surface of a 2 x 2 mu m(2) heterojunction bipolar transistor. The presence of an artifact at the emitter post indicates that accurate temperature measurements are limited to hat surfaces. The FMI measurements obtained for various power dissipations are compared with electrical measurements of the junction temperature. The good agreement between the two techniques suggests that the temperature drop along the emitter post of the device is within a few degrees.