Patterning of micro- and nanometer scale structures by means of nanostencils (shadow masks) is increasingly being used as a simple, clean and low-cost alternative to photolithography. Currently, large area pattern transfer using nanostencil lithography is limited by the mechanical stability of the shadow-mask membrane itself. The reason is that the deposited material induces undesirable stress in the membrane causing excessive bending or breakage and consequent loss in dimensional control. We have developed improved nanostencils with in-situ, local stabilization structures for increased moment of inertia, I. SEM images of membrane structures after Cr deposition are shown for the unstabilized and Si-supported membrane structures. It is confirmed that the membrane stabilization structures significantly reduces out-of-plane deformation of the membrane.