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Power consumption and the thermal wall have become the major factors limiting the speed of very-large-scale integration (VLSI) circuits, while interconnect is becoming a primary power consumer. These factors bring new demands on the communication architecture of system-on-chips (SoCs). High bandwidth is desired to enhance parallelism for better performance, and the power efficiency on this bandwidth is critical to the overall SoC power consumption. Current bus architectures such as AMBA, Coreconnect, and Avalon are convenient for designers but not efficient on power. This paper proposes a physical synthesis scheme for on-chip buses and bus matrices to minimize the power consumption, without changing the interface or arbitration protocols. By using a bus gating technique, data transactions can take shortest paths on chip, reducing the power consumption of bus wires to minimal. Routing resource and bandwidth capacity are also optimized by the construction of a shortest-path Steiner graph, wire sharing among multiple data transactions, and wire reduction heuristics on the Steiner graph. Experiments indicate that the gated bus from our synthesis flow can save more than 90% dynamic power on average data transactions in current AMBA bus systems, which is about 5-10% of total SoC power consumption, based on comparable amount of chip area and routing resources.