  Nanoscale superconducting quantum interference devices (SQUIDs) are
fabricated in-situ from a single Bi$_{0.26}$Sb$_{1.74}$Te$_{3}$ nanoribbon that
is defined using selective-area growth and contacted with superconducting Nb
electrodes via a shadow mask technique. We present $h/(2e)$ magnetic flux
periodic interference in both, fully and non-fully proximitized nanoribbons.
The pronounced oscillations are explained by interference effects of coherent
transport through topological surface states surrounding the cross-section of
the nanoribbon.
