A novel spectral imaging ellipsometer based on a mono‐axial power spectrograph has been developed for one‐dimensional spectroscopic measurement of patterned structures. To obtain the imaging data of a patterned sample using ellipsometry can be realized by conventional ellipsometers with 2‐dimesional (2D) scanning sample stage or 2D imaging ellipsometers with imaging optics. The former has major advantage of high precision, but it has disadvantage in the measurement speed due to mechanical scanning. The latter uses a 2D imaging detector to extract 3D spatial information. So it must be the type of a single‐wavelength ellipsometer. Analyzing the spatial structure of a multi‐layered sample needs the spectroscopic measurement at each spatial point. Therefore we have developed a real‐time spectral imaging ellipsometer base on a mono‐axial spectrograph which can give not only 1D spatial information but also 1D spectroscopic information. The mono‐axial spectrograph is simply composed of entrance slit, holographic transmission grating, and cylindrical doublet as shown in Figure. The custom‐built spectral imaging ellipsometer has the spectral resolution of 10 nm and the spatial resolution of 200 &mgr;m. In the near future the spatial resolution will be enhanced by adopting a focusing optics. © 2003 American Institute of Physics