For full solid-state key telephone systems, high breakover voltage IC switches, which can connect to the central office lines directly and form a large scale matrix within a small volume, has been desired. Firstly, this paper compares several kinds of IC switches, which are suitable for formation of speech path matrix and shows that the photo-coupled PNPN crosspoint switch, connected in bridge format, is superier to the others because of low transmission loss, small matrix volume, reliability against lightning, self-latching speech path during power suspension and NTT technical requirements satisfaction. Secondly, the paper clarifies required electrical conditions for the PNPN element and the crosspoint circuit. They are breakover voltage above 300 V, dv/dt firing torelance above 160 V/0.1 µs, on-resistance within 9 Ω, less than 0.97 V forward voltage drop and restricting the reverse leak current which flows in the optically triggered PNPN element. Next, the IC switch structure is described, along with available technologies to satisfy the electrical requirements, such as canal isolation, highly efficient photo coupling structure and light shielding of anode junction. Actual IC switch characteristics satisfy all required values.