The structural and phase diagrams of β/γ near-eutectic Ni-Co-Cr-Al alloys subjected to various heat treatments are constructed using the electron microscopic data obtained in our earlier works and the reported data. The composition range Ni-(12-20) wt % Co-(17-20) wt % Cr-(9.5-10.5) wt % Al is found to correspond to the eutectic alloys that have high heat resistance and a structure with high thermal stability.