In this work, we present an on chip microelectromechanical system based on an array of cantilevers for mass detection. The sensor transducer, using polysilicon as structural layer, has been integrated monolithically with the CMOS circuitry. Arrays of four and eight resonant cantilevers excited and detected electrically through the integrated circuit have been fabricated. Submicrometric dimensions of the integrated cantilevers allow obtaining a mass sensitivity of 28Hz/fg being the expected mass resolution in vacuum in the femtogram range. In this paper, we present the MEMS fabrication process, some examples of the integrated cantilevers arrays and the electrical test of the on chip MEMS system to characterize the performance of the system for mass sensing purposes.