As the scaling-down of semiconductor processing technology goes on, it is urgent to find the successor of silicon-based materials since the severe short channel effect lowers down their energy efficiency as logic devices. Owing to its atomic thickness and van der Waals surface, two-dimensional semiconductors have received huge attention in this area, among which Bi ₂O ₂Se has achieved a good trade-off among the carrier mobility, stability and costing. However, the synthesis of Bi ₂O ₂Se need some polarized substrates, which hinders its processing and application. Here, a Bi ₂O ₂Se layer with 25 µm in size and 51.0 nm in thickness is directly synthesized on a silicon substrate via chemical vapor deposition . A Field-effect transistor with a carrier mobility of 80.0 cm ²/(V·s) and phototransistor with a photoresponsivity of 2.45×10 ⁴A/W and a photogain of 6×10 ⁴is also demonstrated, which hpossesses quite outstanding photodetection performance. Nevertheless, the high dark current and low on/off ratio brought by the large thickness leads to a fair detectivity (5×10 ¹⁰Jones). All in all, , although silicon substrate brings convenience in device fabricating, it is still needed to further optimizing the growth and integrating more applications of various two-dimensional materials .