Cosputtered amorphous thin films consisting of Ti and Si were crystallized to the C49 TiSi2 phase at temperatures of about 390 °C. Prolonged annealing of the crystalline C49 TiSi2 phase at higher temperatures resulted in a gradual decrease in resistivity. We investigated the changes in microstructure which were associated with this slow decrease of the resistivity of the C49 phase. In situ resistivity and Hall‐effect measurements, electron microscopy, and x‐ray diffraction were used. It was demonstrated that the slow decrease in resistivity of the crystalline C49 phase was associated with a decreasing stacking fault density (typically 2×106 cm-1) and a decreasing density of point defects. The presence of point defects was found to be related to stoichiometry deviations. Polymorphous crystallization of a slightly Si‐rich sample was found to result in a supersaturated solid solution of Si in C49 TiSi2. It was proposed that the phase field of the C49 phase is significantly wider than that of the equilibrium C54 phase. The reproducably low resistivity of the C54 TiSi2 polytype was due to the elimination of practically all stacking faults and point defects.