Doubly-clamped nanowire electromechanical resonators that can be used to generate parametric oscillations and feedback self-sustained oscillations. The nanowire electromechanical resonators can be made using conventional NEMS and CMOS fabrication methods. In very thin nanowire structures (sub-micron-meter in width), additive piezoresistance patterning and fabrication can be highly difficult and thus need to be avoided. This invention shows that, in piezoresistive nanowires with homogeneous material composition and symmetric structures, no conventional and additive piezoresistance loops are needed. Using AC and DC drive signals, and bias signals of controlled frequency and amplitude, output signals having a variety of frequencies can be obtained. Various examples of such resonators and their theory of operation are described.