We study the existence and stability of periodic solutions of a canonical mass-spring model of electrostatically actuated Micro-Electro-Mechanical System (MEMS) by means of classical topological techniques like a priori bounds, Leray–Schauder degree and topological index. A saddle-node bifurcation is revealed, in analogy with the autonomous case. A quantitative estimation of the bifurcation value in terms of realistic values of the involved parameters can be made.