A sensor membrane structure is provided. The sensor membrane structure includes a substrate, a first insulating layer, and a device layer. The substrate has a first surface and a second surface that is opposite to the first surface. A cavity is formed on the first surface, an opening is formed on the second surface, and the cavity communicates with the opening. The cavity and the opening penetrate the substrate in a direction that is perpendicular to the first surface. The first insulating layer is disposed on the first surface of the substrate. The device layer is disposed on the first insulating layer. The first insulating layer is disposed for protecting the sensor membrane structure from overetched and remain stable during the etching process, increasing the yield of the sensor membrane structure.