We demonstrated the effectiveness of plasma-free HCl gas etching on a SiO2-masked (010) β-Ga2O3 substrate. The etching process proceeded anisotropically in the window areas, resulting in the fabrication of holes or trenches that were surrounded by etching-resistant (100)- and (01)-faceted sidewalls. When we etched in the striped windows along [001], we were able to create fins and trenches with flat (100)-faceted vertical sidewalls and slightly rough {310}-faceted inclined bottom corners. The vertical-to-horizontal etching ratio was as high as ∼11–14. Our findings indicate that HCl etching is a promising method for fabricating high-aspect-ratio fins/trenches on (010) substrates without causing plasma damage.