Embodiments of the invention provide a semiconductor device and a fabrication method for a semiconductor device that includes the processes of forming multiple gates on a silicon substrate, forming a gate spacer having a positive slope at the gate spacer edge, depositing a polysilicon layer on the silicon substrate between the gates, etching a portion of the polysilicon layer to form an opening exposing a portion of the silicon substrate, and forming an inter-insulation layer to the exposed portion of the silicon substrate to fill the opening. Using an annealing process applied to a layer in the gate spacer, the etch selectivity can be selectively controlled and consequently, the degree of slope at the gate spacer edge is predetermined.