The electron energy and density in a diamond microwave plasma‐assisted chemical vapor deposition reactor are determined using a double‐electrostatic‐probe technique. For a reactor feed gas composition of 2% CH4, 1% O2in H2, electron temperatures of 6 eV and electron densities of ∼1.0×1011cm−3were measured. These values are consistent with optical emission spectroscopic results. The electron temperature is not strongly dependent on the amount of O2added to the reactor feed mixture, indicating that the plasma essentially retains the energetic parameters of a hydrogen plasma.