The photoelectrical glass-ceramics GeSe2-Sb2Se3-CuI which contain self-organized heterojunction networks is a novel and promising photovoltaic material. Here, a series of these glass-ceramics with gradually changed GeSe2/Sb2Se3 ratios are studied. The composition dependence of the crystallization behavior is analyzed by differential scanning calorimetry and compared with the composition dependence of the photoelectrical properties. It is revealed that the glass-ceramics with evident photoelectrical response show two common features in differential scanning calorimetry curves: an overlapping crystallization peak attributed to the coprecipitation of Cu2GeSe3 and Sb2Se3, and peak profiles showing the characteristics of direct impingement growth. Based on these results, it is concluded that the formation of the heterojunction networks in the photoelectrical glass-ceramics is ascribed to the kinetically allowed eutectoid crystallization of Cu2GeSe3 and Sb2Se3.