Diverter-less intake for supersonic aircraft is examined as a modern design technique of propulsion/airframe integration. In this study, a design guideline for the compression ramp in an external compression supersonic intake mounted on a low diverter or without diverter is examined by CFD analysis. We pursue the optimum configuration of the ramp which minimizes the boundary-layer flowing into intake without failing to decelerate the supersonic flow captured by an intake. The flow field over a single-stage rectangular wedge mounted on a flat surface was investigated under the free stream Mach number of 1.6. The results show that, under a given cross-sectional area of the intake throat, the width and angle of the ramp are important parameters to determine the optimum configuration. In order to decrease the mass flow rate of boundary-layer which flows into an intake, the ramp width should be small as long as the minimum decelerating demand is satisfied. The excessive large angle is not allowed because it induces substantial pressure loss of the main flow. In case of diverter-less configuration, the ramp width should be designed smaller than that in case of configuration with diverter to minimize the incoming boundary-layer.