In critical-dimension measurement using critical-dimension measurement scanning electron microscopes (CD-SEMs), measurement variation due to a long-term instability of CD-SEM cannot be disregarded to achieve a measurement reproducibility of 3 nm, which is required for next-generation subquarter-micron large scale integrations. We have evaluated the long-term stability of the Hitachi S-8820 CD-SEM by using a calibration standard, which has 0.24 mu m pitch structures. The results of our evaluation have demonstrated that the use of the calibration standard for CD-SEMs was effective for checking the instability of instruments, which might produce inaccuracy and imprecision of CD measurements, and measurement error due to instrumentation of 1 nm can be achieved by precise control of instrumental parameters using the calibration standard.