We have investigated optical properties and electrical properties of electrically degraded ZnSe layers by heavy Al doping, where their electron concentrations lie in the range of 7×1017–6×1018 cm-3. Low-temperature photoluminescence exhibits two dominant radiative trap centers of 1.97 eV (RD1) and 2.25 eV (RD2), which are ascribed to VZn-related complex defects. Deep-level-transient spectroscopy shows two electron-trap centers at 0.16 eV (ND1) and 0.80 eV (ND2) below the conduction-band minimum. On the other hand, it is found that RD2 is dominant in relatively lightly doped ZnSe:Al layers below 7×1018 cm-3 and RD1 is dominant in more heavily doped layers near 1×1019 cm-3, while ND1 and ND2 are independent of Al doping concentration and their trap densities are estimated be below 3×1016 cm-3. This indicates that RD1 and RD2 cause the carrier compensation in heavily doped ZnSe:Al layers. Their electron transport mechanism can be explained by ionized-impurity scattering mechanism.