Abstract In this work, in order to check the suitability of CMOS Active Pixel Sensors (APS) detectors for vertexing/tracking applications, four stacked CMOS APS sensors featuring 256×256 pixels with 10×10 μm 2 size have been tested at the INFN Beam Test Facility (BFT), Frascati (Rome). For this purpose, a dedicated mechanical and electrical set-up has been devised and implemented, allowing for the simultaneous read-out of four sensors arranged in a stacked structure. A compact and fast system (up to 64 MHz read-out clock) based on external ADCs and FPGA allows for the PC communication through USB2.0. Preliminary results in terms of track reconstructions of electrons of different energies (up to 496 MeV) are presented. This work has been carried out within the framework of the SHARPS project, supported by INFN.