A capacitor with alterable capacitance for changing the impedance of a section of a coplanar waveguide, which may be used in particular as a high-frequency microswitch, is provided. A ground lead and a signal lead interrupted by an electroconductive connection which is self-supporting at least in some areas are provided, the capacitor including the electroconductive connection and an additional electroconductive connection connected to the ground lead. A structure connected to the electroconductive connection is provided, which is designed in such a manner that it reduces mechanical stresses which occurs in the electroconductive connection. An exemplary embodiment of the device provides for the electroconductive connection to be made of a material having coefficients of thermal expansion similar to that of silicon and a high modulus of elasticity compared to metals, in particular of molybdenum, tantalum or tungsten. The two exemplary embodiments may be combined.