This study presents a systematic experimental investigation into the thermal-fluidic characteristics of a novel manifold ring-microchannel heat sink operating under periodic heat flux conditions. The research focuses on analyzing the coupled thermal responses and flow instability phenomena across a wide range of disturbance frequencies (0.5–500 Hz) and mass flux conditions (1.0–3.44 g/s). Through comprehensive measurements of wall temperature distributions, pressure fluctuations, and high-speed visualization of bubble dynamics, the work reveals several key findings regarding system behavior under transient thermal loading. The results demonstrate distinct frequency-dependent responses, where low-frequency excitations produce large-amplitude temperature oscillations while high-frequency inputs lead to rapid thermal stabilization. Detailed analysis of the two-phase flow characteristics shows that pressure variations exhibit greater sensitivity to thermal disturbances compared to mass flux changes, particularly in low-frequency regimes. The study further examines how increasing the mass flux modifies the system’s dynamic response, including reductions in oscillation amplitudes and changes in spectral energy distribution patterns. High-speed imaging captures complex bubble growth and collapse processes, highlighting how intermediate frequency disturbances generate the most intense interfacial activity. The experimental data also document spontaneous overheating mitigation mechanisms through bubble dynamics in the specially designed manifold ring-microchannel heat sink. These findings contribute to fundamental understanding of transient two-phase heat transfer processes and provide valuable insights for optimizing thermal management systems in electronic cooling applications.