A method of measuring a step height of a device using a scanning electron microscope (SEM), the method may include providing a device which comprises a first region and a second region, wherein a step is formed between the first region and the second region, obtaining a SEM image of the device by photographing the device using a SEM, wherein the SEM image comprises a first SEM image region for the first region and a second SEM image region for the second region, converting the SEM image into a gray-level histogram and calculating a first peak value related to the first SEM image region and a second peak value related to the second SEM image region, wherein the first peak value and the second peak value are repeatedly calculated by varying a focal length of the SEM, and determining a height of the step by analyzing a trend of changes in the first peak value according to changes in the focal length and a trend of changes in the second peak value according to the changes in the focal length.