In　this　paper,　the　frequency　response　characteristics　of　the　photodetector(PD)　were　studied　considering　intrinsic　and　extrinsic　effects.　Then　we　designed　the　interdigitated　p-i-n　PD　on　Silicon-on-Insulator　(S01)　and　epitaxial　(EPI)　substrates　with　photosensitive　area　of　30-mu　m　diameter,　fabricated　by　CMOS　process.　The　2-mu　m　finger-spacing　devices　exhibited　a　205　MHz　bandwidth　at　a　reverse　bias　of　3　V　processed　on　2-pm　SOI　substrates.　EPI　devices　with　1　pm　finger　spacing　exhibited　a　131　MHz　bandwidth　under-3　V.　Responsivity　of　0.051　AW　and　0.21　A/W　were　measured　at　850　tun　on　SOI　and　EPI　substrates,　respectively.　Compared　with　the　bulk　silicon　PD,　the　bandwidth　is　greatly　improved.　The　PD　gains　the　high　cost　performance　ratio,　which　can　he　widely　used　in　short　distance　communication　such　as　visible　light　communication　and　free　space　optical　communication.