A micromechanical capacitive z-acceleration sensor. The sensor includes a substrate with a main extension plane and a layer sequence which is parallel to the extension plane, and includes a first polysilicon layer, a second polysilicon layer, and a third polysilicon layer, with a movable micromechanical structure having a seismic mass which can be deflected in a straight line in a first direction perpendicular to the extension plane. The movable micromechanical structure is formed in the second polysilicon layer and the third polysilicon layer. A measuring capacitance is formed between the seismic mass and a measuring electrode formed in the first polysilicon layer. A reference capacitance is formed between lower and upper reference electrodes, which are formed in the first and polysilicon layers, respectively. As viewed in the first direction, the movable micromechanical structure at least partially overlaps the upper reference electrode.