With the development of ocean energy exploration, reliable and low cost semi-submersible platforms are expected to develop. The maximum pitching amplitude of a floater for floating offshore wind turbine should be less than a few degrees to avoid fatigue failure. In this paper, a novel conceptual design of a new type semi-submersible with suspensions for suppressing the pitch motion is presented. Many wave energy dissipation devices, such as add-onwave energy converters to a floating platform, could be regarded as the suspension system in our design. Firstly, linear models are applied to approximate the radiation forces and wave exciting forces so that the whole motion system is represented by a state-space model. Then, we show that design of suspensions leads to synthesize a controller via solving a constrained H∞ optimization problem. Finally, numerical examples are performed to verify the design and it can be shown that the pitch motion of the semi-submersible platform is remarkably reduced.