This study focused on optimizing a vapor-phase hydrofluoric acid etching process to eliminate stiction occurrence during NEMS release. A dedicated lithography mask was designed to assess the performance of the HF vapor process from a stiction standpoint. This mask features all typical structures found in NEMS and MEMS devices (beams, combs, ground planes). For each structure type, representative dimensions vary (for instance: for a fixed beam width, length ranges from 1 to 200μm). Therefore, the release efficiency for a given process is the maximum size of a specific structure that is released without observing any stiction. Several design-of-experiments were successively carried out in order to compute different models representing the stiction occurrence for a given structure design as a function of process parameters (HF and IPA flowrates, temperature). The main output parameter in DOEs was the release efficiency on different beam designs, which is characterized on SOI wafers patterned with the mask described above. Though, for industrial considerations, etch rate and etch uniformity were also taken into account. Model accuracies were then tested experimentally and the best fit was found to be a second degree model including only the HF and IPA flowrates as factors, the temperature being held constant at 20°C. Thanks to this model, optimization was then carried out by targeting the highest release performance achievable. A new set of process parameters was figured out which improved release efficiency by 15% while the etch rate is four times faster than the former process used.