The authors investigate the optical resonance modes (ORMs) generated in semiconductor microtubes of spiral symmetry by using finite-difference time-domain methods. Even though the tube-wall thickness is much smaller than the light wavelength, modes having an electric field parallel to the tube wall can loop around the tube periphery as ORMs. In addition, the degenerated ORMs present in conventional cylindrical cavities such as whispering gallery modes are broken and separated into two modes due to the spiral asymmetry of the rolled-up microtubes.