In this paper the present state of development of high efficiency silicon solar cells for use at high concentration levels (20 X – 100 X) is described. The design factors and process steps leading to the best performance within the available process technology are analyzed. The cell efficiency has exceeded 20%, and possibilities are discussed for further improvements in efficiency, for larger-area cells and for operation at higher insolation levels (greater than or equal to 100 X). The measured temperature coefficients and the testing requirements are given. Also, some production run results are given to show the possibility of scale-up of the process developed for these cells.