We study shock wave-boundary layer interaction in Mach 2.5 flow over a forward-facing step. The step height (h) used for the present study is twice the incoming boundary layer thickness (δ). The experimental results from schlieren visualization and wall pressure measurements are given in the present work. High-speed schlieren images are acquired at 10,000 fps per second. Micro-second exposure schlieren visualization images show the unsteady nature of the separation shock. Schlieren images show that the separation shock foot motion in the streamwise direction is of the order of the step height (h). Spectra of the separation shock location obtained from schlieren images show that the dominant frequency is two orders of magnitude smaller than the characteristic frequency of the incoming boundary layer (U∞/δ). Instantaneous schlieren images show the formation of a series of compression waves inside the boundary layer and these waves combine to form a separation shock wave outside the boundary layer, with the nature of these shocks varying with time. Downstream of the separation shock one can see the wall shear layer, reattachment shock, and an expansion fan. Spectra of unsteady wall pressure data near the separation shock location also show a dominant frequency that is two orders of magnitude smaller than the characteristic frequency of the incoming boundary layer. The dominant frequency seen from high-speed schlieren and unsteady wall pressure data is found to be in good agreement, and hence high-speed schlieren can be used to study the. © 2020 by Begell House, Inc.