A method of manufacturing a semiconductor device structure, such as a FinFET device structure, is provided. The method begins by providing a substrate comprising a bulk semiconductor material, a first conductive fin structure formed from the bulk semiconductor material, and a second conductive fin structure formed from the bulk semiconductor material. The first conductive fin structure and the second conductive fin structure are separated by a gap. Next, spacers are formed in the gap and adjacent to the first conductive fin structure and the second conductive fin structure. Thereafter, an etching step etches the bulk semiconductor material, using the spacers as an etch mask, to form an isolation trench in the bulk semiconductor material. A dielectric material is formed in the isolation trench, over the spacers, over the first conductive fin structure, and over the second conductive fin structure. Thereafter, at least a portion of the dielectric material and at least a portion of the spacers are etched away to expose an upper section of the first conductive fin structure and an upper section of the second conductive fin structure, while preserving the dielectric material in the isolation trench. Following these steps, the fabrication of the devices is completed in a conventional manner.