We probe electromechanical properties of InAs nanowire (diameter ∼100nm) resonators where the suspended nanowire is also the active channel of a field-effect transistor. We observe and explain the nonmonotonic dispersion of the resonant frequency with dc gate voltage (Vgdc). The effect of electronic screening on the properties of the resonator can be seen in the amplitude. We observe the mixing of mechanical modes with V gdc. We also experimentally probe and quantitatively explain the hysteretic nonlinear properties, as a function of Vg dc, of the resonator using the Duffing equation. © 2010 The American Physical Society.