Semiconductor devices and methods of manufacture thereof are disclosed. In some embodiments, a method of manufacturing a semiconductor device includes forming an etch stop layer over a workpiece. The etch stop layer has an etch selectivity to a material layer of the workpiece of greater than about 4 to about 30. The method includes forming an insulating material layer over the etch stop layer, and patterning the insulating material layer using the etch stop layer as an etch stop.