1. A semiconductor apparatus comprising: first, second, and third semiconductor chips piled up one after another; and first, second, and third penetration-electrode groups for establishing communication among the first to the third semiconductor chips, wherein the first semiconductor chip transmits a request signal to the second semiconductor chip via the first penetration-electrode group, and the second semiconductor chip sends back a response signal to the first semiconductor chip via the second penetration-electrode group in response to the request signal, and wherein the first semiconductor chip transmits a request signal to the third semiconductor chip via the first penetration-electrode group, and the third semiconductor chip sends back a response signal to the first semiconductor chip via the third penetration-electrode group in response to the request signal.