A three-dimensional numerical study is performed to explore the effect of a pulsed rectangular heating element (also denoted as thermal bump) in a Mach 1.5 laminar flat plate boundary layer. The thermal bump is modeled as a time-dependent step surface temperature rise. The thermal bump generates a series of counter-rotating streamwise vortices formed at the four edges of the element. When the bump is pulsed, vortex shedding is observed. These vortices interact with each other, generating a complicated vortical field, and grow in the spanwise direction with the downstream distance. Results show that the vertical perturbation velocity plays a key role in generating a lifting effect to sustain the horizontal disturbances. The streamwise velocity perturbation produces a low-speed region downstream of the centerline and a high-speed region on each side of the bump. The disturbance energy shows that the streamwise kinetic disturbance energy dominates over other components.