A semiconductor device on a SOI and a method for manufacturing the same are provided. The semiconductor device includes a semiconductor wafer having a SOI structure including an insulating layer having a predetermined thickness and a monocrystalline silicon layer formed on the insulating layer, an isolation insulating layer formed on the insulating layer on the semiconductor wafer, a gate comprised of a gate dielectric layer and a gate conductive layer, which are sequentially stacked on the monocrystalline silicon layer, insulating layer spacers formed at the sidewalls of the gate, and a source junction and a drain junction asymmetrically formed at either side of the gate between the isolation insulating layer spacers and the insulating layer. In the semiconductor device formed on a SOI, source and drain junctions are formed at either side of a gate to be asymmetrical, and thus a ground of a transistor is formed on the SOI, and thus the electrical characteristics of the semiconductor device are improved.