High-density microeletronics increasingly requires advanced cooling strategies to ensure reliable, high performance. The use of substrates with high thermal conductivity, e.g., diamond, is an attractive approach to managing heat dissipation; however, the fabrication of metal circuitry on diamond films is hindered by the chemical inertness of the surface, In this paper, we present an additive, channel constrained metallization process for the fabrication of metal circuitry on diamond surfaces. We address several issues specific to this application, including photoresist lithography and metal adhesion on subatrates with significant surface roughness (peak-to-valley roughness similar to 4 to 5 mu m) and the fabrication of circuitry with sufficient electrical conductivity. Fabricated circuitry exhibits suitable resolution (similar to 10 mu m), metal thickness (greater than or equal to 2 mu m), effective electrical resistivity (similar to 10 mu Omega-cm for composite Ni/Cu/Au traces), and adhesion (passes tape peel test) fur operation at power levels of at least 22 W (i.e., 1 A, 22 V) without failure or delamination. Thermal modeling and IR images of operating circuitry show an similar to 50% decrease in component junction temperature rise (from ambient) on diamond (k similar to 1200 W/m K) vs. alumina (k similar to 20 W/m K), consistent with thermal conductivity differences between these substrate materials.