International audienceThe SPIRAL2 installation is being built in order to study rare elements through the production of radioactive isotopes. Its injector, a superconducting linear accelerator (LINAC) is designed to provide very high intensity (up to ~ 1014 particles/s) beams of deuterons and stable ions between carbon and uranium. The “Super Separator Spectrometer” (S3) was designed to separate and mass-analyse recoils from the various induced fusion-evaporation reactions in order to enable nuclear structure studies of proton-rich rare isotopes around 100Sn and in the region of the Super Heavy Elements. A new optimized focal plan detection system called SIRIUS for “Spectroscopy and Identification of Rare Isotopes Using S3” is developed to within the SIRIUS collaboration. The new generation windowless large area silicon-box developed in this framework is discussed in this article. We present the simulations done in order to determine the best geometry and layout for this large area silicon detector assembly