In this paper, we describe the design and fabrication of a thermionic scanning electron microscope (SEM) and examine its characteristics analytically. In the design process, the dimensions and capacity of the SEM components, such as the electron column, lenses, and apertures, were determined using finite element analysis. All components were integrated systematically during fabrication in order to achieve the maximum performance by adjusting the lens parameters, high voltage source, and image calibration methods. As a result, a thermionic SEM image with high resolution was achieved. We discuss the primary considerations required to achieve a high-performance image.