In this paper, a new integrated design method – the convex integrated design (CID) method – is introduced and applied to the design of a semi-active suspension system. The closed-loop system is required to simultaneously satisfy four closed-loop performance specifications: car body acceleration, suspension deflection, tyre dynamic load and control effort. With a simple two-stage algorithm, the mechanical structure design parameter, as the stiffness of the suspension spring in the semi-active suspension system, and the closed-loop controller are determined with the CID method. This leads to a closed-loop suspension system which in simulation, is shown to satisfy all four closed-loop performance specifications. Then the suspension system is redesigned with two closed-loop performance specifications, car body acceleration and energy of control effort, and through experimentation, the closed-loop performance is verified on suspension test bed. Both simulation and experimental results verify the effectiveness of the CID method, with two closed-loop performance specifications.