A novel hydrogenation-assisted deep reactive ion etching of silicon is reported. The process uses sequential hydrogen-assisted passivation and plasma etching at low-density plasma powers to stimulate the vertical removal of the exposed Si substrate. The main feature of this technique is the sequential alternation of the electrodes while switching between different gases. Three-dimensional structures with aspect ratios in excess of 40:1 and features as small as 0.7 mum have been realized. The net etch rate is about 0.25 mum/min, although higher rates are expected to be achievable.