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 (MEAs) positioned in contact with the neural tissue. Thanks to microelectronics' microfabrication technologies, it now becomes possible to build high density MEAs 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 system with integrated electronics allowing simultaneous recording and stimulation of neural networks. Both actions are performed independently on all channels.