An epitaxial substrate for an electronic device, in which a lateral direction of the substrate is defined as a main current conducting direction and a warp configuration of the epitaxial substrate is adequately controlled, as well as a method of producing the epitaxial substrate. Specifically, the epitaxial substrate for an electron device, including: a Si single crystal substrate; and a Group III nitride laminated body formed by epitaxially growing plural Group III nitride layers on the Si single crystal substrate, wherein a lateral direction of the epitaxial substrate is defined as a main current conducting direction, is characterized in that the Si single crystal substrate is a p-type substrate having a specific resistance value of not larger than 0.01 Ω·cm.