Bisphenol A-based epoxy resin (DGEBA) was modified with bisphenol A polycarbonate (PC), by either a physical or chemical process, and thermally cured with 4,4’-diaminodiphenyl sulfone, tetraethylenepentamine, and anhydride. The phase separation in the PC/epoxy blends was controlled by varying the composition, and the PC-epoxy reaction, and utilizing curing agents of different reactivity. A single phase morphology was achieved by accelerating the curing reaction, or introducing PC-epoxy reaction, or eliminating crystallization of PC. Under certain conditions, PC spherulites are able to form, in company with the formation of epoxy networks. Curing of the epoxy resin modified the crystallization mechanism, the melting behaviour and the morphology. The nuclei are likely to be pre-existing high molecular weight PC chains and are formed by the special interaction between PC molecules and the primary network. Low molecular weight epoxy resins increase the crystallization rate. The internal fractionation changes by PC chain scission during the melt blending process has an important influence on the crystallization. The spherulite morphology fixed by semi-IPN structure subjected a loss of order by annealing. It is suggested that hydrogen bonding and graft reaction in this kind of PC/epoxy semi-IPN is the key to controlling phase separation and morphology.