We develop enabling technologies addressing the needs of deterministic assembly. In addition to our previous body of work on nanowires, our most recent approach allows a truly three-dimensional fabrication of silicon nanowires with a critical dimension of 20 nm within thick silicon layers. The technique is composed of two etching mechanisms, where the first shallow etch defines a nanoscale surface protrusion, which – upon proper sidewall passivation- is released through a subsequent deep etch step. The technique is demonstrated with an extreme etch depth of 40 microns. Thanks to the monolithic nature of the developed nanofabrication technology, nanowires’ piezoresistive response can be characterized under both quasi-static and resonant conditions with future implications in sensor applications.