This article is focused on the optimization and design of a multipass branching microchannel heat sink for high heat flux electronics cooling applications. A multiphysics topology optimization method is used to arrive at two different branching channel solutions for the cooling of a heated plate. These optimization results are combined and synthesized into a unique multipass manifold microchannel heat sink design that has both jet and channel based characteristics. Numerical experiments for a representative electronics package were completed to evaluate the heat sink thermal and fluid performance. It is found that the derived cold plate exhibits favorable heat transfer with low pressure drop due to multiple passes through the branching microchannels. In addition to numerical results, ongoing prototype development for concept validation is described.