Remarkable improvement in resolution when observing critical dimensions in semiconductor inspection by using a newly- developed deep-UV optical microscope is presented. At present, while scanning electron microscope (SEM) is the only imaging tool for less than 0.20-micron geometry, improvement in resolution of optical microscope has strongly been desired because of its easier operations and less damage including feature. Simulation of resolution to be achieve indicated that deep-UV wavelength only clearly resolve less than 0.15-micron geometry and images acquired at 266nm in the following experiment well agreed with the simulation. An objective lens especially for deep-UV, laser light source, illumination and imaging optics, and image detection device were built on a conventional microscope stand. This high-resolution microscope may extend the field of optical inspection and even open up new inspection applications.