A series of experiments has been carried out to study the etching prop
erties of silicon in hydrazine, with particular emphasis on the applic
ability of the etchant in micromachining of microsensors. A new method
of suppressing the etching of aluminium in hydrazine is presented 'an
d a simple theory to account for the observed effects is proposed. Pra
ctical aspects involved in the setting up of hydrazine etching equipme
nt are also discussed.