The increasing in chip power has led to an increasing demand for two-phase immersion cooling. This paper reports series boiling experiments of dual-chip in vertical with a pin-finned heatsink using HFE-7100. And the boiling curves, photography and total heat transfer coefficients are compared with the boiling of single-chip. Results show that the heat flux of bottom chip is slightly higher than that of top chip in surface superheats lower than 16.5 K, while the heat flux of top chip is higher than the bottom chip at high superheats. And the top chip is 9.3 K colder than the bottom chip while it reaching critical heat flux (CHF). The coalescence bubbles quickly detach driven by the bubbles flow from bottom chip, resulting in the decreases of the surface superheat ΔTsat and the increases of the total heat transfer coefficients hT of top chip. The superheat of top chip in dual-chip is 6.3 K lower than that of the single-chip in CHF. And the hT of top chip in dual-chip is 11% (~0.15 W/cm2K) higher than that of the single-chip in ΔTsat = 21.3 K. As for unbalanced load, the superheat increases of top chip decrease from 4.1 K to 0.6 K with a stepped rise of heat flux in 4 W/cm2 due to the reinforcement from the bottom chip. The rising flow disturbs the coalescence bubbles on pin-finned, improving the departure frequency and narrowing dry areas. Therefore, the enhancement mainly exists in top chip or upper chips with high surface superheats.