[en] Growth mechanism and temperature of monoclinic gallium oxide (β‐Ga${}_2$O${}_3$) films grown by ozone molecular beam epitaxy (MBE) are investigated herein. Phase-pure ($\stackrel{¯<!--\; ??\; -->}{2}$01) β‐Ga${}_2$O${}_3$ films can be grown on c-plane sapphire substrates when the growth temperature exceeds 500 °C, and the grain size increases with the increase in the growth temperature. Sixfold rotational domains are obtained based on the epitaxial relationships (Ga${}_2$O${}_3$<010>//Al${}_2$O${}_3$<1$\stackrel{¯<!--\; ??\; -->}{1}$00> and Ga${}_2$O${}_3$<102>//Al${}_2$O${}_3$<11$\stackrel{¯<!--\; ??\; -->}{2}$0>). For the film grown at 700 °C, the threefold facets are observed for the first time, which are resulted from the easy-cleaved (100) plane and rotational domains. In addition, the cathodoluminescence spectra of the β‐Ga${}_2$O${}_3$ films show that the proportion of ultraviolet emission increases with the increase in the growth temperature, which is attributed to the modulation of defect. Finally, the growth rate can be modulated by the ratio of Ga flux and ozone pressure. A reference is provided for heteroepitaxy of β‐Ga${}_2$O${}_3$ films and better understanding of the ozone MBE growth mechanism of oxides. (© 2020 Wiley‐VCH GmbH)