The design rule of semiconductor devices in 1984s, when optical microscope was used for critical dimension measurement of device patterns, was around 1.3 µm. Instead of the optical microscope which did not provide enough resolution for the further device shrinkage, CD-SEM (Critical-Dimension Scanning Electron Microscope) was used for 1 µm or smaller design rule. This report introduces recent CD-SEM technologies and future prospect for such smaller design rule. Furthermore, evaluation of CD-measurement accuracy is introduced. It consists of short-term and long-term repeatabilities and tool-to-tool matching. A new linewidth-measurement algorithm is implemented for better short-term repeatability. A method of contrast-gradient is used for tool-to-tool matching. A traceable standard-sample for magnification calibration is also used.