A flexible membrane (12) of an integrated circuit chip test probe is provided with raised contact features (14) on one side arranged in the pattern of contact pads of the chip to be tested. During manufacture, the membrane, in the area of its raised contact features, is specifically shaped by applying a vacuum to the outside of the membrane and casting a solid resilient elastomer (26) in place on the other side of the membrane to act as a shape retaining solid backup and to provide an anti-drape (226) shaped membrane (212) or to ensure planarity (326) of the ends of the membrane contact features (314). The vacuum may be used to pull the membrane and its contacts against a shape defining mandrel (60, 260, 360) while the elastomer is cast into place.