MashadiGemawati, SriHasriatiHerlinawati, Hesy2016-02-172016-02-172016-02-172248-9851wahyu sari yenihttp://www.iphsci.com/math_sci_vol_therteen_iss_one_two_octuber_december_twozerofifteen.htmlhttp://repository.unri.ac.id/xmlui/handle/123456789/7924Suppose that ABCD is a quadrilateral. Then there will be 4 pieces of semiexcircle on the quadrilateral. In this paper, we will discuss how to determine the length of the radii of the semi-excircle, but previously we will also be discussed how to determine the length of 4 new sides formed from the extension of the sides on □ABCD which has no parallel sidesensemi-excircle of quadrilateralsemi-Gergonnetangential quadrilateralradii of excircleUR-Scientific Work Lecturer