A method for integrating complementary metal-oxide-semiconductor (CMOS) devices with a microelectromechanical systems (MEMS) device using a flat surface above a sacrificial layer is provided. In some embodiments, a back-end-of-line (BEOL) interconnect structure is formed covering a semiconductor substrate, where the BEOL interconnect structure comprises a first dielectric region. A sacrificial layer is formed over the first dielectric region, and a second dielectric region is formed covering the sacrificial layer and the first dielectric region. A planarization is performed into an upper surface of the second dielectric region to planarize the upper surface. A MEMS structure is formed on the planar upper surface of the second dielectric region. A cavity etch is performed into the sacrificial layer, through the MEMS structure, to remove the sacrificial layer and to form a cavity in place of the sacrificial layer. An integrated circuit (IC) resulting from the method is also provided.