The instability of flow boiling in the microchannel results in a reduction in thermal performance and undesired fluctuations in surface temperature. The high rate of vapor bubble generation and its rapid growth block the confined flow passage of the microchannel and develop high resistance to flow. Periodic changes in flow regime and inefficient vapor venting mechanism lead to backflow and increase the dryout time period in the microchannel heat sink results reduction in overall heat transfer coefficient of microchannel heat sinks at high heat flux. In this work, novel mechanism of inlet plenum flow restrictor is use to control the reverse flow and provide mass flow inventory at inlet plenum to minimize the dryout period. Additionally, the flow passage area from the outlet of the microchannels to the outlet plenum is gradually increased by providing a taper angle to the outlet manifold passage, which reduces the accommodation of excessive vapour in the manifold passage and lowers the generation of high pressure in the outlet manifold. Subcooled flow boiling experiment has been carried out with DI-water in a copper substrate containing 44 parallel microchannels having high aspect ratio (channel width 230µm and height 500µm) for mass flux of 320 kg/m²s and heat flux range of 28-81 W/cm². The inlet fluid temperature is maintained at 78 ± 1 °C (subcooling of 22 ± 1 °C). It is observed that providing inlet plenum flow restrictor, effectively reduces the fluctuations in surface temperature by 64%, fluctuations in inlet fluid temperature by 51% and maintain stable inlet temperature of the coolant at higher heat flux. Moreover, a potential of flow restrictor at the inlet plenum is indicated by an increase in heat transfer coefficient. As a result, the flow boiling in microchannels becomes more stable, and thermal management for microelectronic cooling becomes more promising and effective.