An inspection method for a semiconductor device is disclosed. The method includes providing a semiconductor device, performing heat treatment on the semiconductor device, and inspecting the semiconductor device utilizing electron beam to acquire an analysis image. The semiconductor device comprises a substrate, a plurality of gate electrodes protruding on the substrate, a blanket dielectric layer overlying the substrate and gate electrodes, and a plurality of polycrystalline silicon plugs, respectively disposed on the substrate between the gate electrodes, in the dielectric layer. A piping defect is detected by the analysis image showing an area with voltage contrast difference.