A new method of detecting a T-topped profile in resist patterns is described. This method can determine a T-topped tendency from only a single top-down CD-SEM image. The idea is based on the relationship between the cross-sectional pattern profile and the shape of the bright area near the pattern edge in the top-down image. Two kinds of index for a T-topped tendency are defined using line-edge roughness, width of the bright area, and the correlation coefficient between the left and right borders of the area. Both indices agreed well with actual cross-sectional profiles of various resist patterns. In addition, it is found that these indices can be used to estimate defocus in the photolithography process.