Most set expansion algorithms assume to acquire new instances of different semantic categories independently even when we have seed instances of multiple semantic categories. However, in the setting of set expansion with multiple semantic categories, we might leverage other types of prior knowledge about semantic categories. In this paper, we present a method of set expansion when ontological information related to target semantic categories is available. More specifically, the proposed method makes use of sibling relations between semantic categories as an additional type of prior knowledge. We demonstrate the effectiveness of sibling relations in set expansion on the dataset in which instances and sibling relations are extracted from Wikipedia in a semi-automatic manner.