To facilitate wide adoption of handheld devices for mobile Internet access, it is important to enable the ”develop once and use everywhere” concept. This means that a Web page can be developed in HTML for presentation on desktop machines, and then be automatically adapted and displayed on any devices including handheld devices. In this paper, we present a mediator Web service that automatically adapts a Web page into suitable formats based on receiving devices. Our underpinning is a hierarchical semantic meta model associated with a semantic ontology. They guide in partitioning a Web page into semantically coherent segments, which refer to atomic units encapsulating semantically coherent elements in a Web page. Our experimental results demonstrate that our semantic segment detection algorithm helps in transforming Web pages into semantic-retained formats suitable to be displayed on handheld devices.