The advent of supercomputers with many computational nodes each with its own independent memory makes possible very fast computations. Our work is focused on the development of electronic structure techniques for the solution of Grand Challenge-size molecules containing hundreds of atoms. Our efforts have resulted in a scalable direct-SCF (self-consistent-field) Fock matrix construction kernel that is portable and efficient. Good parallel performance is obtained by allowing asynchronous communications and using a distributed data model. These requirements are easily handled by using the Global Array (GA) software library developed for this project. This algorithm has been incorporated into the new program NWChem.