The effect of oxygen termination of diamond surfaces on the interface thermal conductance between Ag–3Si and diamonds is investigated in dependence of temperature by measuring thermal conductivity in the temperature range from 4 K up to ambient. Composites for O-terminated diamonds exhibit a marked maximum of 960 W m− 1 K− 1 at roughly 150 K. Calculation of the interface conductance by the differential effective medium (DEM) scheme obtained marked difference between H- and O-terminated diamond surfaces in composites and is supported by AFM force distance measurements on native, H-terminated, and O-terminated diamond single crystal (100) surfaces. O-termination can be easily induced by immersing diamonds in hot aqua regia solution.