In this paper, we review the synthesis of intercalated silicon clathrates and their physical properties. More particularly, their high pressure–high temperature synthesis and their superconductivity properties are detailed. Si-clathrates are cage-structures allowing for the ultra-degenerated intercalation of donor or acceptor atoms. Their physical properties are both governed by the sp 3 tetrahedral bonding and by the guest–host interactions. The endohedral intercalation gives rise to the observation of a number of unique behaviors like their extreme high pressure stability as well as their unique type of isostructural phase transformations. Three types of Si-clathrates exist corresponding to different stoichiometries: type-I M 8 Si 46 (with M=Na, K, Rb Ba, Sr, Ca or I), type-II M x Si 136 with M=Na or Cs and type-III Ba 24 Si 100 (sp 2 /sp 3 system). The Si-clathrates are phonon-mediated BCS superconductors. Only type-I and type-III are superconducting with critical temperatures ranging from T c =1.55 K (Ba 24 Si 100 ) to 8 K (Ba 8 Si 46 ). In the type-I, superconductivity is an intrinsic property of the sp 3 silicon network. When Ba is replaced by Sr or Ca, the electronic density of states at the Fermi level decreases, involving the reduction of T c . For Ba 24 Si 100 , the importance of the mixed sp 2 /sp 3 character of the Si-bonds in the explanation of its lower T c is still under debate.