A method of forming a semiconductor device includes forming a first layer on a semiconductor fin; forming a mask on the first layer, the mask being thicker on a top of the semiconductor fin than along a sidewall of the semiconductor fin. The first layer is thinned along the sidewall of the semiconductor fin using the mask. A second layer is formed on the semiconductor fin, the second layer covering the mask and the first layer. A dummy gate layer is formed on the semiconductor fin and patterned to expose a top surface of the semiconductor fin.