Spinodal decomposition of the A(x)(III)B(1-x)(III)C(y)(V)D(1-y)(V) quaternary alloys as the result of the internal stresses, coherency stress and transformations of the chemical bonds is presented. The alloys are described in the strictly regular approximation. Ranges of spinodal decomposition of the InxGa1-xAsyP1-y, InxGa1-xSbyAs1-y and AlxGa1-xSbyAs1-y quaternary alloys lattice-matched to their conventional substrates are estimated. It is shown that the temperatures of spinodal decomposition of the InxGa1-xAsyP1-y, InxGa1-xSbyAs1-y and AlxGa1-xSbyAs1-y should be smaller than their growth temperatures.