A method embodiment includes providing a MEMS wafer comprising an oxide layer, a MEMS substrate, a polysilicon layer. A carrier wafer comprising a first cavity formed using isotropic etching is bonded to the MEMS, wherein the first cavity is aligned with an exposed first portion of the polysilicon layer. The MEMS substrate is patterned, and portions of the sacrificial oxide layer are removed to form a first and second MEMS structure. A cap wafer including a second cavity is bonded to the MEMS wafer, wherein the bonding creates a first sealed cavity including the second cavity aligned to the first MEMS structure, and wherein the second MEMS structure is disposed between a second portion of the polysilicon layer and the cap wafer. Portions of the carrier wafer are removed so that first cavity acts as a channel to ambient pressure for the first MEMS structure.