Periodic mesoporous organosilicas (PMOs) with 2D-hexagonal structure have been prepared by the sol–gel route in acidic conditions from a bissilylated reactive as a silica-modified source, namely 1,2-bis(triethoxysilyl)ethane (BTEE), and Pluronic P123 non-ionic surfactant as a templating agent. Pyrolysis of the PMO material was performed under inert atmosphere up to 1000 C in order to assess the possibility to transform the hybrid network into a porous SiOC glass network. The pyrolysis process has been mainly followed by 29 Si and 13 C solid state NMR. Thermal degradation of the pore network was followed by XRD and TEM and measured by N 2 adsorption–desorption experiments. This study shows that despite the Si–C bonds cleavage occurring after 600 C causes a phase separation into silica and free carbon, an ordered structure is retained up to 1000 C with a remaining specific surface area.