Silicon nanopillars, fabricated by electron beam lithography and reactive ion etching, were size-reduced using laser-assisted electrochemical etching in a dilute hydrofluoric acid solution. The progressing size reduction was followed by scanning electron microscopy down to final diameters of ∼15 nm. By varying the voltage bias, it was found that etching could be directed primarily at the pillar top (7 V) or at the pillar base (−0.6 V) whereas in an intermediate regime, conformal etching could be obtained. From the rate of volume change during etching, it was concluded that holes, participating in the dissolution reaction, were primarily generated within the pillar volume. The corresponding effective dissolution valence was ∼5–9, indicating substantial recombination losses within the pillar.