TECSTAR has made significant progress in improving the efficiency and yield of multijunction (Cascade(R)) solar cells. TECSTAR has produced 27.0% efficient 2 cm x 2 cm Cascade(R) cells through improvements in material quality and cell structures. Radiation performance of these cells has also improved. The remaining power after 1E15 e/cm(2), 1 MeV electron irradiation is greater than 80%. In addition, TECSTAR has successfully developed an integral bypass diode, grown monolithically with the Cascade" cell. No degradation in the diode performance after subjected to 1E15e(-)/cm(2), 1 MeV electron irradiation and no degradation in the CIC assemblies after subjected to 3000 cycles of dark reverse test. (C) 2001 Published by Elsevier Science B.V. All rights reserved.