The effects of micro-structured surfaces installed on the internal walls of a pre-chamber gasoline engine on the near-wall flow field are numerically investigated. In such engines, achieving high thermal efficiency requires both enhanced air–fuel mixing during jet injection into the main chamber and suppression of cooling losses from the internal walls. Funaki et al. attempted to realize these two objectives simultaneously by introducing rib-like obstacles in the jet impingement region. They reported a maximum heat transfer reduction of approximately 28% compared with a smooth wall; however, their rib configuration resulted in an approximately 13% increase in the root-mean-square (RMS) concentration fluctuation relative to the smooth-wall case, indicating degraded mixing performance. In addition, the effective range of geometric parameters remained limited. In the present study, rib structures oriented perpendicular to the jet direction are investigated through a detailed parametric analysis. Multiple ribs with different heights are arranged, and the spacing between ribs is freely adjusted, introducing a new rib arrangement concept with significantly greater geometric freedom than previous designs. By appropriately modifying the rib spacing, jet diffusion is promoted in regions away from the wall, leading to improved scalar mixing. As a result, the proposed configuration achieves a maximum reduction of approximately 6% in the mixing index relative to the smooth-wall case. In addition, interactions among ribs of different heights induce an upward deflection of the jet, increasing the distance between the jet and the wall surface. This mechanism significantly reduces jet–wall contact, thereby suppressing near-wall thermal transport. Consequently, a maximum reduction in heat transfer of approximately 71% is achieved compared with the smooth-wall case. These results demonstrate that appropriate selection of rib geometry enables simultaneous enhancement of mixing and suppression of heat transfer in pre-chamber gasoline engines. Future work will focus on further optimization by varying additional geometric parameters to achieve finer control of jet dynamics and thermal transport.