The behavior of shock wave reflection under varying levels of flow rarefaction is investigated using the Direct Simulation Monte Carlo (DSMC) method. An internal supersonic flow of monoatomic Argon gas over a sudden ramp geometry is considered as the test case. The simulations are carried out with the dsmcFoam solver, a DSMC module of the OpenFOAM package. Initially, the shock reflection phenomenon in the continuum limit is verified through comparison with conventional Computational Fluid Dynamics (CFD) simulations based on the Navier–Stokes equations and with analytical predictions from gas dynamics theory. Following this validation, the influence of rarefaction is examined by progressively decreasing the upstream flow density to achieve different Knudsen number regimes. The results demonstrate that increased rarefaction leads to significant thickening of both the incident and reflected shock waves, with the effect being more pronounced for the reflected shock. Furthermore, the reflected shock exhibits stronger deviations from its continuum counterpart in terms of shape and sharpness. At the shock–ramp interaction points, where a straight shock profile is expected under continuum conditions, the simulations reveal the formation of a curved shock front. This curvature is attributed to the emergence of localized non-equilibrium flow regions, where the assumptions of local thermodynamic equilibrium no longer hold. These findings provide new insights into shock structure modification in rarefied gas flows, relevant to microscale devices and high-altitude hypersonic flight applications.