In order to understand the dynamics of large neural networks, where information is widely distributed over thousands of cells, one of today’s challenges is to successfully record the simultaneous activities of as many neurons as possible. This is made possible by using microelectrodes arrays (MEA) positioned in contact with the neural tissue. Thanks to microelectronics’ microfabrication technologies, it now becomes possible to build high-density MEA containing several hundreds of microelectrodes. However, increasing the number of electrodes using conventional electronics is difficult to achieve. Moreover, high-density devices addressing all channels independently for simultaneous recording and stimulation are not readily available. Here, we present a 256-channel in vitro MEA data acquisition system with integrated electronics allowing simultaneous recording and stimulation of neural networks for in vitro and in vivo applications. This integration is a first step towards an implantable device for a neural prosthesis.