"Cloud Computing" refers to the emerging environment providing software and hardware services over the Internet or Cloud on demand. These services are provided to millions of Cloud users, in particular Mobile users, by thousands of servers in the data centres. Server power consumption and costs are becoming a great concern in the data centres in which the servers are built with high end, expensive and power-hungry CPUs. We are now reaching the limit of voltage scaling preventing further power reductions. In the absence of voltage scaling, chips in the future may have hundreds of cores, but to maintain a power envelope, these cores have to be embedded cores having orders of magnitude lower power consumption.Server applications are rich with client-request and memory-level parallelism. Each client is primarily served by a simple core with high-bandwidth/low-latency access to memory. 3D-stacking of on-chip DRAM on many embedded cores will provide high memory bandwidth with less power consumption while enabling scalability for green future servers.We propose EuroCloud - 3D "Server-on-Chip" built using many ARM cores and integrating 3D DRAM to provide a very dense low power server, and targeting the Cloud workloads. EuroCloud targets 10x improvement in cost- and energy-efficiency compared to current state-of-the-art servers. This will scale to hundreds of cores in a single server, and make a 1M core data centre feasible in the future. Thus, designing the 3D Server-on-Chip will provide us with capabilities to build super-efficient, environmentally clean and compact data centres in Europe aiming at green Cloud services. Thus, pioneering the green data centres will further strengthen the European leadership and excellence in green computing.