Silicon photonic integration is an enabling technology for power- and cost-effective optical interconnects in exascale performance computers and datacenters which require extremely low power consumption and dense integration for a higher interface bandwidth density. In this paper, we experimentally demonstrate a fully integrated optical transceiver network on a silicon substrate using heterogeneous integration. High performance on-chip lasers, modulators and photodetectors are enabled by transferring III-V materials to a pre-patterned silicon substrate. Wavelength division multiplexed transceivers with eight wavelength channels are monolithically-integrated on a single chip, forming an optical network-on-chip circuit with total transmission capacity up to 8×8×40 Gbps, and bandwidth density over 2 Tbps/cm. We show that the heterogeneous silicon integration provides the design flexibility and scalability for high-speed optical communication systems.