Si-based nanocomposite has attracted attention because Si exhibits a large power factor as much as Bi2Te3 alloy and is environmental friendly and low cost element. Towards high ZT, in Si-based nanocomposite, thermal conducticvity has been attempted to be reduced by nanocyrstalization and percipitation of secondary compound in Si matrix. In this study, in order to enhance the power factor of Si-based nanocomposite by employing Ytterbium silicide as a second compound with high power factor, we demonstrated that Silicon and Ytterbium silicide-based nanocomposite is able to be synthesized by rapid-solidification at eutectic point between Si and YbSi2. Si-YbSi2 nanocomposites exhibit a hierarchical structure with 10nm Si layer in grain boundary of 50nm YbSi2 crystal grains and Si crystal grains of more than 100nm.