A remarkable stability in the sharp photo-current peak at 570 nm was found when p-CuSCN semiconductor photocathode was sensitized with double-dye LB films of rhodamine-C-18 (R-C-18) monolayers and methylviolet-C-18 (M-C-18) monolayers. At first, M-C-18 four monolayers were deposited on p-CuSCN and then, R-C-18 four monolayers were deposited on M-C-18 monolayers to make an molecular arrangement on the semiconductor (LB-(R-C-18(4)/M-C-18(4))/p-CuSCN). Such a photo-cathode exhibited a remarkable stability of steady-state photo-current in (10(-2) M) KI+ (10(-4) M) I-2 aqueous solution of pH = 6.5, where the quantum efficiency reached was 45%, as estimated by correcting the dye absorption in the sharp photo-current peak at 570 nm. When four monolayers of M-C-18 and four monolayers of R-C-18 were separated with an arachidic acid LB films, sharp photo-current peak and its stability gradually decreased. This remarkable stability may be due to an efficient energy transfer process and an efficient charge separation caused by a strong interaction between the parallel electron-vibration planes of both M-C-18 and R-C-18 molecules.