An imaging ellipsometer using a LiNbO3 electrooptic crystal was developed for in situ measurement. The basic configuration of polarizer-compensator-window(1)-sample-window(2)-analyzer system was employed. Ellipsometric imaging was made from intensity images measured at 4-step phase modulation. Ex situ and in situ measurements were performed for a silicon wafer and a SiO2 film thermally grown on the silicon substrate to examine the functionality of this ellipsometer. The measurement results show the feasibility of the application of this system to the qualitative in situ measurements of samples. (C) 2014 Elsevier B.V. All rights reserved.