A novel, compact 48-channel optical transceiver module has been designed and fabricated. At the heart of the assembly is a "holey" Optochip - a single-chip CMOS transceiver integrated circuit (IC) with 24 receiver and 24 laser driver circuits each with a corresponding through- substrate optical via (hole). The holes enable 24-channel 850-nm VCSEL and photodiode (PD) arrays to be directly flip- chip soldered to the CMOS IC with substrate-side optical I/O through the otherwise absorbing bulk silicon substrate. This feature of the holey Optochip not only facilitates direct fiber- coupling to a standard 4 x 12 MMF (multimode fiber) array through a 2-lens optical system, but also maximizes highspeed performance through the close integration of the VCSEL and PD devices with the CMOS amplifier circuits. Furthermore, the holey Optochip is directly compatible with current mass-produced 850-nm VCSELs and photodiodes. These Optochips were packaged into complete modules by flip-chip soldering to high-density, high-speed organic carriers using a process very similar to standard C4 soldering used for electrical ICs. The full assembly of the Optomodule involves further attachment to a pin grid array pluggable connector. Electrical characterization of Optomodules plugged into a test circuit board incorporating the socket half of the connector was carried out and dc electrical characterization showed fully operational 24 transmitter (TX) + 24 receiver (RX) Optomodules with uniform performance for all devices within the module. High-speed characterization of all 48-channels (ch) showed good performance up to 12.5 Gb/s/ch. At 12.5Gb/s/ch, an aggregate data rate 300 Gb/s TX + 300 Gb/s RX is provided by the holey Optomodule. © 2010 IEEE.