As the thermal density of electronic devices rapidly increases, the demand for heat spreaders capable of dissipating high heat fluxes exceeding 150 W/cm² is emphasized in thermal management applications. Boiling-driven heat spreaders, which operate based on boiling instead of evaporation, circulate the working fluid through bubble pumping without wick structures, thus offering higher operational limits than conventional vapor chambers. So, research on boiling-driven heat spreaders is gaining new attention. However, existing studies have focused on the thermal performance of boiling-driven heat spreaders at high heat fluxes without evaluating their spreading thermal resistance and temperature uniformity index (TUI). Since the essence of a heat spreader is to disperse concentrated heat over a wide area, evaluating these metrics is essential. A boiling-driven heat spreader with dimensions of 90 mm × 90 mm × 2 mm was fabricated in this study. The experimental results showed that the junction temperature remained below 79℃ at a high heat flux of 240 W/cm². The spreading thermal resistance recorded values of 0.1 K/W at heat fluxes above 100 W/cm², which is 43% lower than that of a copper plate of the same shape. Particularly, in the vertical up direction, the minimum thermal resistance of 0.088 K/W was achieved at a heat flux of 200 W/cm². The TUI of the condenser section showed lower values than copper at all heat fluxes above 6 W/cm², and no significant changes were observed at heat fluxes above 200 W/cm² due to bubble pumping. These results confirm that the boiling-driven heat spreader operates stably even at high heat fluxes and suggest its effective application for thermal management in high-heat-flux electronic devices.