We present novel microelectromechanical chemical sensors for the detection of volatile organic compounds based on electrostatically actuated, nanometer-thin, freestanding membranes of organically cross-linked gold nanoparticles. The sensors employ quasi-static deflection amplitudes or resonance frequency shifts of the membranes as highly sensitive sensing signals and are capable of detecting analytes at concentrations down to the low ppm range. We show that the devices can further be utilized for analyte discrimination. Additionally, we demonstrate that freestanding GNP membranes can be used for the fabrication of highly sensitive resistive pressure sensors.