A compound semiconductor epitaxial substrate and a process for producing the same are provided. The compound semiconductor epitaxial substrate comprises a single crystal substrate, a lattice mismatch compound semiconductor layer and a stress compensation layer, wherein the lattice mismatch compound semiconductor layer and the stress compensation layer are disposed on the identical surface side of the single crystal substrate, there is no occurrence of lattice relaxation in the lattice mismatch compound semiconductor layer, as well as the stress compensation layer, and Ls representing the lattice constant of the single crystal substrate, Lm representing the lattice constant of the lattice mismatch compound semiconductor layer, and Lc representing the lattice constant of the stress compensation layer satisfy the formula (1a) or (1b). Lm Lm>Ls>Lc  (2a)