A method of making a semiconductor device, the method includes forming an active region in a substrate. The method further includes forming a first gate structure over the active region, where the forming the first gate structure includes forming a first interfacial layer. An entirety of a top surface of the first interfacial layer is a curved convex surface. Furthermore, the method includes forming a first high-k dielectric over the first interfacial layer. Additionally, the method includes forming a first gate electrode over a first portion of the first high-k dielectric and surrounded by a second portion of the first high-k dielectric.