A detailed experimental study has been done to understand the shock wave-turbulent boundary layer interaction (SWTBLI) over a forward-facing step (FFS) of height (h) in a Mach 2.5 flow using particle-image velocimetry (PIV). In addition to PIV, high-speed schlieren and surface oil flow visualization have been studied. Flow separation using surface oil flow visualization was observed around 4.1 step heights upstream of the step face. High-speed schlieren measurements show that the shock oscillates with a peak frequency of approximately 1000 Hz, which is two orders smaller than the characteristic frequency of the incoming boundary layer. Instantaneous PIV velocity vector fields show that the shock location is related to the separation bubble formed ahead of the forward-facing step. © Springer India 2017.