Semiconducting n-type diamond can be fabricated using phosphorus as a substitutional donor dopant. The dopant activation energy level at 0.58eV is deep. At high dopant concentrations of 10 20 cm −3 the activation energy reduces to less than 0.05eV. Phosphorus doping at concentrations of 10 20 cm −3 or higher has been achieved with epitaxial growth on the (111) diamond crystallographic surface. In this work epitaxial growth of diamond with high phosphorus concentrations exceeding 10 20 cm −3 is performed using a microwave plasma-assisted chemical vapor deposition process with process conditions that include a pressure of 160Torr. This pressure is higher than previous phosphorus doping reports of (111) surface diamond growth. The other growth conditions include a feedgas mixture of 0.25% methane and 500ppm phosphine in hydrogen, and a substrate temperature of 950–1000°C. The measured growth rate was 1.25μm/h. The room temperature resistivity of the heavily phosphorus doped diamond was 120–150Ω-cm and the activation energy was 0.027eV.