User interface description languages (UIDL) are high-level languages allowing to model user interfaces (UI). Their purpose is to ease the design of UIs. They are widely used, including to develop critical interactive systems. Nevertheless, the problem of verifying systems developed with UIDLs is barely addressed in the literature. The first step is to provide a formal semantics using an appropriate theory. We claim that the bigraphs theory is a good candidate theory. In this short paper, presenting a work in progress, we introduce the common features of UIDLs and show how bigraphs could be used to define UIDLs semantics and help with UI verification.