We present for the first time a three-dimensional (3-D) Si CMOS interconnection system consisting of three layers of optically interconnected hybrid integrated Si CMOS transceivers. The transceivers were fabricated using 0.8-μm digital Si CMOS foundry circuits and were integrated with long wavelength InP-based emitters and detectors for through-Si vertical optical interconnections. The optical transmitter operated with a digital input and optical output with operation speeds up to 155 Mb/s. The optical receiver operated with an external optical input and a digital output up to 155 Mb/s. The transceivers were stacked to form 3-D through-Si vertical optical interconnections and a fabricated three-layer stack demonstrated optical interconnections between the three layers with operational speed of 1 Mb/s and bit-error rate of 10-9.