For several decades, researchers have actively pursued the exploration of enhanced surfaces to improve passive twophase heat transfer. In this particular study, a tubular surface with a unique semi-closed microstructure is developed using a deformational cutting method. The primary objective is to examine the enhanced performance of a 2×3 semi-closed microstructure tube bundle (TB) in contrast to a smooth 2×3 TB, while considering variations in pitch to diameter ratios (P/D) and heat flux. The findings indicate that the semi-closed microstructure TB surpasses the smooth TBs in terms of performance, owing to its ability to achieve lower boiling initiation wall superheat and provide a larger surface area. The microstructure TB exhibits a more than 100% improvement in effectiveness compared to the corresponding smooth TB, surpassing it by over two-fold. In conclusion, this research underscores the potential of the semi-closed microstructure TB as an effective and cost-efficient technology for passive twophase heat transfer. The present work finds direct application in heat exchangers and nuclear industries.