A bonded semiconductor wafer provided with a single crystal silicon layer on a main surface, wherein the bonded semiconductor wafer has a base wafer composed of a silicon single crystal, and the bonded semiconductor wafer has a first dielectric layer, a polycrystalline silicon layer, a second dielectric layer, and the single crystal silicon layer above the base wafer in this order, with a bonding plane lying between the polycrystalline silicon layer and the second dielectric layer; and wherein a carrier trap layer is formed between the base wafer and the dielectric layer. This provides a bonded semiconductor wafer of a trap-rich type SOI substrate wherein the base wafer can be prevented from lowering the specific resistance due to impurities and influence of electric charge in the BOX oxide film, distortion of radio-frequency fundamental signals and crosstalk signals from one circuit to another circuit are decreased, and the mass-productivity is excellent.