Prismatic stacking faults in α-Ga2O3 films on (0001) Al2O3 substrates are investigated using transmission electron microscopy (TEM). The studied films are grown by halide vapor phase epitaxy (HVPE) up to 1.3 µm in thickness. The initial growth stage results in threading dislocations (TDs) of an average density of 1010 cm–2. The majority of the TDs are identified as 1/3 < 1\(\overline{1}\)00 > partial edge and 1/3 < 1\(\overline{1}\)01 > perfect mixed types using g∙b = 0 invisibility criterion under two-beam diffraction conditions. The edge component of Burgers vector is determined by the Burgers circuit procedure using high-resolution TEM images of dislocation cores. It is suggested that 1/3 < 1\(\overline{1}\)01 > partial dislocations may arise as a result of dissociation of 1/3 < 2\(\overline{1}\)\(\overline{1}\)0 > erfect dislocations which leads to the emergence of prismatic stacking faults in the films.