With the use of silicon micromachining, an inorganic membrane sieve for microfiltration has been constructed having a silicon nitride membrane layer with thickness typically 1 μm and perforations typically between 0.5 μm and 10 μm in diameter. As a support a [Left angle bracket]100[Right Angle Bracket]-silicon wafer with openings of 1000 μm in diameter has been used. The thin silicon nitride layer is deposited on an initially dense support by means of a suitable chemical vapor deposition method (LPCVD). Perforations in the membrane layer are obtained with use of standard photo lithography and reactive ion etching (RIE). The deflection and maximum load of the membrane sieves are calculated in a first approximation. Experiments to measure the maximum load of silicon-rich silicon nitride membranes have confirmed this approximation.