A process for producing at least one air gap in a microstructure, which includes the supply of a microstructure comprising at least one gap filled with a sacrificial material, this gap being limited over at least part of its surface by an impermeable membrane but which may be rendered permeable by the action of a chemical etchant, this etchant also being capable of degrading the sacrificial material and the contacting of the microstructure with said chemical etchant in order to make the membrane permeable and degrade the sacrificial material, and the removal of the chemical etchant from the microstructure and in which the chemical etchant is a fluid containing hydrofluoric acid and/or ammonium fluoride. Applications include microelectronics and micro-technology.