Clean and even millimetre-size electron-transparent plan-view specimens of ZnSe/GaAs with and without the GaAs substrate completing with a lift-off method for GaAs epilayers have been prepared by chemical thinning with a 5:1 (NaOH:H2O2) solution. Cross-sectional specimens of ZnSe/GaAs with very little ion-induced damages and extensive thin area suitable for HREM imaging have been prepared by argon ion milling. Ion-induced damage in ZnSe has virtually been eliminated by progressively decreasing ion voltages to 0.7 kV. Large thin areas result from the glue line of the cross-sectional specimen being shadowed by the GaAs substrate in off-centre single-side ion milling.