A semiconductor device having fins and a method of manufacture are provided. A patterned mask is formed over a substrate. Trenches are formed in the substrate and the trenches are filled with a dielectric material. Thereafter, the patterned mask is removed and one or more etch processes are performed to recess the dielectric material, wherein at least one of the etch processes is an etch process that removes or prevents fences from being formed along sidewalls of the trench. The etch process may be, for example, a plasma etch process using NH3 and NF3, an etch process using a polymer-rich gas, or an H2 etch process.