The authors report the realization of highly featured three-dimensional structures on silicon substrates with a single masking layer using a hydrogen-assisted deep reactive ion etching process. Oxygen, hydrogen, and SF6 are used in a sequential passivation and etching process to achieve high aspect ratio features. By controlling the flows of these gases and the power and timing of each subsequence, it is possible to achieve desired deep vertical etching, controlled underetching, and recovery, yielding three-dimensional features directly on silicon substrates. Etch rates up to 0.75 μm/min have been achieved with a low plasma power density of 1 W/cm2. In addition, features with a controllable underetching and recovery with more than 8 μm in sidewall recession have been achieved. Furthermore, values of aspect ratio higher than 40 can be obtained. The formation of three-dimensional features with nanowall structures is reported.