This paper presents a novel silicon-based and batch-processed MEMS electrostatic transducer for harvesting and converting the energy of vibrations into electrical energy without using an electret layer. Effective conversion from the mechanical-to-electric domains of 61 nW on a 60 M Omega resistive load, under a vibration level of 0.25 g at 250 Hz, has been demonstrated. Rigorous analysis of the efficiency of the harvester is presented, covering issues related with mechanical and electrical operation. Various schemes for the conditioning electronics are discussed and the harvested power measurements using a dc/dc converter are explained in detail. The paper concludes with a comparison with previous electrostatic transducers based on a new simple factor of merit.