Free-running experiments are carried out to make clear the stable running of a semi-submersible high speed ship with wings. The ship is an unconventional new type of high speed ship consisting of a main hull, main and tail wings with flaps, and a strut to support the super-structure. The ship floats as a conventional ship but the downward lifting force makes the ship semi-submerged during the operation condition. The model used is a self-propelled free-running model. The carriage follows the model at a constant speed on which all the controllers are placed. Experiments are carried out not only under the calm condition but also among waves of following and head seas, although all the experiments are limited to the forward running tests. Through the experiments it is made clear that the ship can run stably by the control of flaps except under the following sea condition. The induced motions by waves are notably reduced by the submergence. The thrust estimated from the number of revolution of propellers is almost same as the measured resistance and no appreciable increments in the resistance are experienced even among waves. It may be necessary to study more on the flow phenomena and the forces acting on the hull under the following sea condition. Although all the knowledge is limited to the model level, it can be concluded that such an unconventional new type of high speed ship is promising from the hydrodynamic aspects.