We report adhesion, growth, and differentiation of mouse neural cells on ultra-thin films of an organic semiconductor, pentacene. We demonstrate that i) pentacene is structurally and morphologically stable upon prolonged contact with water, physiological buffer, and cell culture medium; ii) neural stem cells adhere to pentacene and remain viable on it for at least 15 days; iii) densely interconnected neural networks and glial cells develop on the pentacene surface after several days. This implies that adhesion proteins secreted by the cells find suitable adsorption loci to anchor the cells. Pentacene is also a suitable substrate for casting thin layers of cell adhesion molecules, such as laminin and poly-L-lysine. Our results show that pentacene, albeit being an aromatic molecule, allows neurons to adhere to and grow on it, which is possibly due to its tightly packed solid state structure. This structure remains unaltered upon exposure to water and interfacial force exerted by the cells. The integration of living cells into organic semiconductors is an important step towards the development of bio-organic electronic transducers of cellular signals from neural networks.