Pool boiling from a surface featuring micropyramidal reentrant cavities (mouth size 40 /spl mu/m) etched in silicon, bonded to a glass substrate, was studied. All experiments were conducted in the dielectric fluid FC-72 at 1 atm. The heat sink is designed to eliminate spreading through the substrate, and back heat loss. Experimentation showed that the critical heat flux was 12.8 W/cm/sup 2/. A high speed camera (400 frames/s) was used to record and quantify the effect of heat flux on departure diameter and bubble emission frequency. Both departure diameter and frequency showed an increasing trend with heat flux. Comparisons with existing literature are also presented.