Hot spots with dimensions of only a few nanometers form in numerous nanoelectronic devices. Based on recent advances in spatial resolution, these hotspots can now be studied by means of Scanning Thermal Microscopy (SThM). Here, we discuss SThM for nanoscale thermometry in comparison with other established thermometry techniques. In situ measurements of semiconductor channels for logic, and phase change memory devices are used to demonstrate today's measurement capabilities. Temperature fields characterize not only energy dissipation in in-tact devices but can also serve to identify device failure and fabrication issues.