Destructive physical analysis (DPA) is one of the reliability evaluation methods, which observes defects and faults in a device, and it can classify the reliability level of the device. After a description of the current method for Au wires, this paper explains the DPA for a Cu wire device. The DPA for semiconductor devices is divided roughly into three steps: a non-destructive inspection, an assembly process inspection, and a wafer process inspection. Investigation of DPA for Cu wire device includes wire material identification, optimization of decapsulation for Cu wire device and wire pull strength test, and observation of package cross-section. From the result, novel sample preparation (embedding a sample in molding package and forming the package to be suitable for cross-sectional observation by ion polishing) enables the observation of the thin alloy layer at the wire/pad interface.