A method of forming a semiconductor device structure is provided. The method includes forming an insulating layer over a semiconductor substrate including a conductive feature, forming an insulating layer with a trench over the semiconductor substrate to expose the conductive feature, and forming a sacrificial liner layer over two opposite sidewalls and a bottom of the trench. Ions are implanted into the conductive feature covered by the sacrificial liner layer, so that a doping region is formed in the conductive feature and has two opposite side edges respectively separated from the two opposite sidewalls of the trench. The sacrificial liner layer is removed after forming the doping region, and a conductive connecting structure is formed in the trench. The two opposite sidewalls of the conductive connecting structure are respectively separated from the two corresponding opposite sidewalls of the trench by an air spacer.