A shallow arched microbeam is actuated parametrically thanks to an axially applied motion. The microbeam is clamped from one side and guided from the other side. The axial motion is generated by an electrostatic force applied to a sliding rigid element directly linked to the arched microbeam through a compliant mechanism that amplifies its motion. The design is used as a mass sensor to detect an infinitesimal amount of a specific gas by its adsorption through a special sensitive coating deposited on top of the arched microbeam. The governing equations are derived using Hamilton’s principle, a Galerkin procedure is applied to extract a reduced order model of the device. The limit-cycle solutions of the dynamic response under an electrostatic harmonic excitation, are calculated using the finite difference method and a continuation technique. The results indicate that masses under 1 pg can be detected with the proposed device.