  We investigate high-redshift galaxy sizes using a semi-analytic model
constructed for the Dark-ages Reionization And Galaxy-formation Observables
from Numerical Simulation project. Our fiducial model, including strong
feedback from supernovae and photoionization background, accurately reproduces
the evolution of the stellar mass function and UV luminosity function. Using
this model, we study the size--luminosity relation of galaxies and find that
the effective radius scales with UV luminosity as $R_\mathrm{e}\propto
L^{0.25}$ at $z{\sim}5$--$9$. We show that recently discovered very luminous
galaxies at $z{\sim}7$ (Bowler et al. 2016) and $z{\sim}11$ (Oesch et al. 2016)
lie on our predicted size--luminosity relations. We find that a significant
fraction of galaxies at $z>8$ will not be resolved by JWST, but GMT will have
the ability to resolve all galaxies in haloes above the atomic cooling limit.
We show that our fiducial model successfully reproduces the redshift evolution
of average galaxy sizes at $z>5$. We also explore galaxy sizes in models
without supernova feedback. The no-supernova feedback models produce galaxy
sizes that are smaller than observations. We therefore confirm that supernova
feedback plays an important role in determining the size--luminosity relation
of galaxies and its redshift evolution during reionization.
