In this paper, we introduce and investigate a new class of Is−open sets, called generalized Is−open sets in ideal topological semigroups a space. We study some properties on this class, such as product and relativity. Further more, the relationships between this class and other known classes are introduced and studied.

Keywords : Open Set; Ideal Topological Space, Topological Semigroup. AMS Classification: Primary 54A05, 16W30.