Compact and passive-alignment 4-channel x 2.5-Gbps optical interconnect modules are developed based on the silicon optical benches (SiOBs) of 5 x 5 mm2. A silicon-based 45 degrees micro-reflector and V-groove arrays are fabricated on the SiOB using anisotropic wet etching. Moreover, high-frequency transmission lines of 4 channel x 2.5 Gbps, and bonding pads with Au/Sn eutectic solder are also deposited on the SiOB. The vertical-cavity surface-emitting laser (VCSEL) array and photo-detector (PD) array are flip-chip assembled on the intended positions. The multi-mode fiber (MMF) ribbons are passively aligned and mounted onto the V-groove arrays. Without the assistance of additional optics, the coupling efficiencies of VCSEL-to-MMF in the transmitting part and MMF-to-PD in the receiving part can be as high as -5.65 and -1.98 dB, respectively, under an optical path of 180 microm. The 1-dB coupling tolerance of greater than +/- 20 microm is achieved for both transmitting and receiving parts. Eye patterns of both parts are demonstrated using 15-bit PRBS at 2.5 Gbps.