The use of semi-submersible platforms has become increasingly popular due to its ability to carry large topsides and the possibility for quayside integration. With recent exploration successes in ultra-deepwater fields of the Gulf of Mexico, major oil and engineering companies are keen to look for a safe, reliable and cost-effective dry-tree option to maximize the value of deepwater field developments. Dry-tree semi-submersible (DTS) emerges as such an option to overcome the water depth and size limits imposed by TLP and Spar, respectively, and enables the platform to carry a large well array and payloads in ultra-deep water. This paper presents the offshore industry’s multi-year efforts to mature two promising semi-submersible platform concepts that can accommodate long-stroke dry-tree risers and have large drilling and production capabilities. Results of technology development and qualification will be highlighted with details on hull performance and hull/riser interfaces. Key structural, mooring and riser analyses and scaled model test results including the long-stroke riser tensioning system will be presented. Remaining challenges that need to be overcome to advance the DTS concepts from “technology acceptance” to “project readiness” will also be discussed.