The present disclosure relates to a method of forming an internal spacer between nanowires in a semiconductor device. The method includes providing a semiconductor structure comprising at least one fin. The at least one fin is comprised of a stack of layers of sacrificial material alternated with layers of nanowire material. The semiconductor structure is comprised of a dummy gate which partly covers the stack of layers of the at least one fin. The method also includes removing at least the sacrificial material next to the dummy gate and oxidizing the sacrificial material and the nanowire material next to the dummy gate. This removal results, respectively, in a spacer oxide and in a nanowire oxide. Additionally, the method includes removing the nanowire oxide until at least a part of the spacer oxide is remaining, wherein the remaining spacer oxide is the internal spacer.