We present millimeter-wave optoelectronic mixers based on Si photodetectors fabricated by the standard 130 nm complementary metal-oxide-semiconductor (CMOS) process. The photodetector and optoelectronic mixer characteristics are investigated in order to optimize their performances. Using the avalanche process in photodetectors at high reverse bias voltages, efficient optoelectronic mixing with low conversion loss at 30 GHz band is obtained. In order to demonstrate the feasibility of applying this mixer for Radio-on-fiber (RoF) applications, detection and frequency up-conversion of optical 5 MS/s, 16 quadrature amplitude modulation (QAM) signals into the 30 GHz band is successfully performed. We believe this is the first report of using CMOS-compatible photodetectors for RoF applications.