To stabilize the electric characteristic of Silicon Thin Film Transistor, reducing the current leakage is most important issue. To reduce the current leakage, many ideas were suggested. But the increse of mask layer also increased the cost. On this research Bird`s Beak process was use to present element. Using Silvaco simulator, it was proven that it was able to reduce current leakage without mask layer. As a result, it was possible to suggest the structure that can reduce the current leakage to 1.39nA without having mask layer increase. Also, I was able to lead the result that electric characteristic (on/off current ratio) was improved compare from conventional structure.