Molten potassium silicide (KSi) has been investigated with a first-principles molecular dynamics technique. The system belongs to the class of I-IV alloys, which have been extensively studied in recent years in view of the anomalous behavior of their structural and thermodynamical properties compared to ideal solutions. A detailed analysis of the ionic trajectories obtained in our computer simulation shows that Zintl-like ions (Si) 44-, present in the solid, tend to lose their identity in the liquid phase and that Si atoms form an extended network with two-, three-, and four-fold coordinated sites. Also, the calculated diffusion constants and power spectra reflect the presence of a different kind of atomic arrangements attained by Si in the melt. The bond between K and Si, characterized in terms of nodal potential energy surfaces, is found to be partially ionic. Accordingly, the computed electronic density of states and electrical conductivity show that the liquid is a semiconductor. Our results can be used to rationalize many experimental findings for molten I-IV alloys. © 1991 American Institute of Physics.