We investigate the effects of parasitic resistance on the performance of silicon avalanche photodetectors (APDs) fabricated in the standard complementary metal-oxide-semiconductor (CMOS) technology. Two types of CMOS-APDs based on the P+/N-well junction having two different parasitic resistances are realized, and their current-voltage characteristics, responsivities, avalanche gains, photodetection frequency responses, and electrical reflection coefficients are measured and compared. In addition, the effect of parasitic resistance on the photodetection bandwidth is analyzed with an equivalent circuit model. It is clearly demonstrated that the parasitic resistance has great effects on the gain and photodetection bandwidth of CMOS-APDs.@en