An epitaxial substrate for electronic devices, in which current flows in a lateral direction and of which warpage configuration is properly controlled, and a method of producing the same. The epitaxial substrate for electronic devices is produced by forming a bonded substrate by bonding a low-resistance Si single crystal substrate and a high-resistance Si single crystal substrate together; forming a buffer as an insulating layer on a surface of the bonded substrate on the high-resistance Si single crystal substrate side; and producing an epitaxial substrate by epitaxially growing a plurality of III-nitride layers on the buffer to form a main laminate. The resistivity of the low-resistance Si single crystal substrate is 100 Ω·cm or less, and the resistivity of the high-resistance Si single crystal substrate is 1000 Ω·cm or more.