PURPOSE: To reduce leakage current of SiC substrate so that it can operate even at a high temperature, by sealing a silicon plate and a single crystal SiC thin piece through an insulating material layer and by providing a silicon layer of a particular thickness doped with no impurity between the single crystal SiC thin piece and the insulating material layer.

CONSTITUTION: An SiC layer 1 which is an element forming layer is provided, an Si layer 5 which is 2μm or less in thickness (ground crystal for enabling SiC layer to be subject to epitaxial growth is provided, an SiO2 layer 2 which is an insulation layer are provided between the Si layer 5 and an Si wafer, 4 which is a supporting substrate on a single crystal SiC substrate. Since the Si layer 5 which is a ground crystal of epitaxial growth is an insulating material such as SiO2, an SiC substrate without any leakage can be obtained if this Si layer 5 can practically be made to be at low resistance. Thus, by keeping the thickness of the ground Si layer 5 to be 2μm or less, the Si layer 5 will have a higher resistance and can be used at high temperature.