A novel 4-step microfabrication process is proposed in this work to prepare arrays of coriented silicalite (SIL-1) micromembranes on customized silicon nitride (Si 3 N x) microsieves. The arrays are integrated on chip and their overall porosity values can be tuned from 1.6% to 19.9%. A low stress Si 3 N x microfabricated sieve has been used as support to reinforce via mechanical interlocking and to reduce the effects of the residual stress during membrane processing. The secondary hydrothermal growth over the Si 3 N x microsieves also changes the SIL-1 chemistry, improving its affinity towards CO 2 adsorption. As a result, the SIL-1/Si 3 N x micromembranes integrated on chip facilitate the preferential permeation of CO 2 in CO 2 /H 2 mixtures, showing a maximum CO 2 /H 2 separation factor of 16.9 and a CO 2 permeance of 8.2•10-7 mol•m −2 •s −1 •Pa −1 at ambient conditions.