Abstract: The Wien-filter type monochromator installed in an FEI Titan 80—300 STEM scanning transmission electron microscope is briefly introduced. It is shown that electron energy-loss spectroscopy (EELS) with an energy resolution better than 0.1 eV can be achieved using the monochromated transmission electron microscope. In the core-loss region, for elements with natural widths of the K-and L-shell energy levels smaller than 0.5 eV, finer near-edge structures can be obtained using the monochromator, and it is also helpful for the understanding of electronic structure. In the low-loss region, high-resolution EELS can be used to determine the bandgaps of semiconductors and the energy shift in the bandgap due to p-type doping.