An evaluation has been conducted to identifiy the structural strength of a rectangular hull semi-submersible configured with eight legs sized 24173 tons and notionally operated in Natuna Sea. In this particular evaluation only the loads in longitudinal direction are consi-dered. Structural responses in the form of shear force and bending moment are computed by the integration of weight distribution with the buoyancy at still water condition as well as due to hogging and sagging waves. Maximum responses are experienced when the semi-submer-sible is excited by a sagging wave having the length equal to the vessel length in the order of 19.18 MN and 259.58 MNm respectively for the shear force and bending moment. The modeling of structural strength is accomplished by the variation of global structure and local structure especially on the column-pontoon connection. Results of the modeling show that for the realistic approximate design namely semi-submersible with a smeared deck the maximum stress on the global structure is found to be some 80.0 MPa and maximum deformation is 15.7 mm. Further the maximum local stress is identified at the connection of the second column to the pontoon that is 46.6 m form the aft end of the hull having value of 182.0 MPa.