Multijunction solar cells based on III-V semiconductors are the most efficient solar cells in the world, and of the established photovoltaic technologies, have the greatest potential for future growth in efficiency. Champion cells with efficiency greater than 40% have been demonstrated by several groups since 2006, and in that same period, the efficiency of cells in mass production has also increased steadily. These devices offer the promise of very competitive solar power systems exploiting the high efficiency under high optical concentration. To this end, Spectrolab is conducting a multi-year program to develop solar cells with still higher efficiency and substantial cost reductions and to fully characterize and qualify them for reliable performance in the field. Development of the fourth production generation with 40% average production efficiency is nearing completion. Cell design and performance will be presented, with a summary of qualification and field test status. Progress in ongoing efforts to automate cell production for cost reduction and increased manufacturing capacity will be discussed. Development of these high-performance multijunction CPV cells is key to the emergence of CPV technology as the lowest cost solar power solution in high DNI areas.