The invention provides a method for use in forming a semiconductor device, the semiconductor device comprising a primary area and a periphery area, the method comprising: providing a substrate on which is situated: a stack in the primary area, the stack comprising a first oxide layer on the substrate, an oxynitride layer on the first oxide layer and a second oxide layer on the oxynitride layer; and a third oxide layer in the periphery area, the method further comprising: substantially removing the second oxide layer from the primary area and the third oxide layer from the periphery area; forming a fourth oxide layer in at least the primary area by an in situ steam generation (ISSG) process; and thereafter forming a polycrystalline semiconductor layer on the fourth oxide layer without any intervening oxidation process steps. Embodiments of the invention, when applied to, for example, the manufacture of SONOS devices, have the advantages that batch-to-batch variation of the thickness of the top blocking oxide of the ONO stack is reduced or eliminated, and ONO line width variation is reduced or eliminated.