Named Entity Extraction is the process of identifying entities (like persons, locations, organizations, etc.) in texts and linking them to related semantic resources. This task is useful in several applications, e.g. for question answering, annotating documents, post-processing of search results, etc. However, existing named entity extraction tools lack an open or easy configuration, although this is very important for building domain-specific applications. For example, supporting a new category of entities, or updating an existing category with additional entities, is either impossible or very laborious. In this paper we show how we can exploit semantic information (Linked Data) at real-time for configuring (handily) a named entity extraction system. We also present X-Link, a fully configurable named entity extraction tool that realizes this approach. Contrary to the existing tools, X-Link allows the user to easily define the categories of entities that are interesting for the application at hand by exploiting one or more (on-line) semantic Knowledge Bases. The user is also able to update a category and specify how to semantically link and enrich the identified entities. This enhanced configurability allows X-Link to be configured for different contexts, for building domain-specific applications (e.g. for identifying drugs in a medical search system or for annotating and exploring fish species in a marine-related web page). To test the approach, we conducted a task-based evaluation with users that demonstrates the usability of the proposed approach, and a case study that demonstrates its feasibility.