The new wavelength‐division solar cell is proposed and its conversion efficiency is calculated. The proposed diode structure can be fabricated by the usual epitaxial growth technique. The considered materials are the combination of InP and In0.58Ga0.42As0.84P0.16having the band‐gap energy of 0.827 eV. The calculated maximum conversion efficiency is 19.5% at air‐mass‐zero (AM0) condition which can be improved by the growth of a CdS window layer on the InP surface. With thick CdS on InP, 22.2% efficiency is obtainable, and when the thickness of CdS is as thin as 0.2 &mgr;m, 27% efficiency will be attainable. Fabrication of the proposed structure with the GaAlAs/GaAs system gives a conversion efficiency of 23.5% which is about the same as conventional heteroface or graded‐band‐gap solar cells. The optimum layer thicknesses that give maximum efficiency are also determined in this paper.