The first anti-tricyclo[3. 1.0.0(2,4)]hexasilane 1 was synthesized as pale yellow crystals. Irradiation (lambda > 370 nm) of I gave its skeletal isomer, tricyclo[2.2.0.0(2,5)]hexasilane 2, in 80% yield. The photochemical [(sigma)2(s) + (sigma)2(s)] cycloreversion of 1 followed by the thermal [(pi)2(s) + (pi)2(a)] cycloaddition to 2 would explain the overall isomerization.