Miscible blends of the crystallizable component poly(ethylene oxide) (PEO) and an amorphous component poly(ether sulfone) (PES) display a double melting behavior. The lower melting endotherm has been attributed to secondary crystallization starting directly after the primary crystallization. The semicrystalline morphology of these PEO/PES blends was studied in detail using synchrotron radiation. Real time small-angle X-ray scattering experiments performed during isothermal crystallization of the PEO/PES blends reveal that secondary crystalline lamellae are formed between the primary lamellae according to the lamellar insertion model. During melting of the secondary lamellae drastic changes occur in the SAXS patterns. On the basis of these observations, a model describing the semicrystalline morphology of PEO/PES blends is proposed. The scattered intensity of PEO/PES blends after the melting of the secondary lamellae is interpreted in terms of a structure factor and a form factor. Model calculations on the form factor of the proposed semicrystalline structure are in agreement with the observed scattering behavior.