The development of nanoelectromechanical systems (NEMS) is likely to open up a broad spectrum of applications in science and technology. In this study, we demonstrate a novel double-transduction principle for silicon nanowire resonators which exploits the depletion charge modulation in a junctionless Field Effect Transistor (FET)-body and the piezoresistive modulation. A mechanical resonance at the very high frequency of 100 MHz is detected in the drain current of the highly doped silicon wire with a cross section down to ~30 nm. We show that the depletion charge modulation provides a ~35 dB increase in output signal-to-noise compared to the second-order piezoresistive detection, which can be separately investigated within the same device. The proposed junctionless resonator stands therefore as a unique and valuable tool for comparing the field effect and the piezoresistive modulation efficiency in the same structure, depending on size and doping. The experimental frequency stability of 10 ppm translates into an estimated mass detection noise floor of ~ 60 kDa at a few seconds integration time in high vacuum and at room temperature. Integrated with conventional semiconductor technology, this device offers new opportunities for NEMS-based sensor and signal processing systems hybridized with CMOS circuitry on a single chip.