This paper proposes an ultra fine-grained run-time power gating of on-chip router, in which power supply to each router component (e.g., VC queue, crossbar MUX, and output latch) can be individually controlled in response to the applied workload. As only the router components which are just transferring a packet are activated, the leakage power of the on-chip network can be reduced to the near-optimal level. However, a certain amount of wakeup latency is required to activate the sleeping components, and the application performance will be degraded. In this paper, we estimate the wakeup latency for each component based on circuit simulations using a 65nm process. Then we propose four early wakeup methods to overcome the wakeup latency. The proposed router with the early wakeup methods is evaluated in terms of the application performance, area, and leakage power. As a result, it reduces the leakage power by 78.9%, at the expense of the 4.3% area and 4.0% performance when we assume a 1GHz operation.