Very high efficiencies have been demonstrated under concentration with silicon solar cells having interdigitated contacts on the backside. However, only laboratory cells of small dimension have reached very high efficiencies. The need for developing a multilevel metallization technology for back contact concentrator solar cells of large area is demonstrated. The particular features required for such a multilevel interconnection are studied and a process using anodic oxidation of aluminum is presented. Back contact silicon solar cells of 0.64 cm2have been processed in this technology resulting in 26.2% efficiencies at 10W/cm2(100 suns AM1.5, 25.5°C). the highest efficiency reported to date for a solar cell of this area. The one-sun efficiency of this cell is 21.7% (AMI.5, 25.2°C). We propose also a new design for the metallization of back contact cells which allows an increase in the size of the cell without increasing the series resistance.