Abstract: As a new high technology, combing the fabrication techniques of IC and compound optical devices, Si-based optoelectronic technology has become more and more attractive. We present results of studies on Si-based optoelectronics carried out in the Instutute of Semiconductors, CAS, including UHV/CVD epitaxy of SiGe/Ge quantum structures and Si-based optoelectronic devices. Type-ⅡSiGe/Si quantum wells and self-organized dots have been successfully grown, and the photoluminescence spectra from the quantum dots were measured as far as 250K. Several Si-based devices, such as resonant cavity enhanced photodiodes, optical modulators and switches, have been fabricated. The quantum efficiency and dark current density of the photodiodes at 1.3μm are 4.2％and 12pA/μm2, respectively. The response time of the 2×2 thermal-optical switches is shorter than 20μs, and the turn-on and turn-off cross-talks are -22dB and -12dB, respectively.