  We performed angle-resolved photoemission spectroscopy studies on a series of
FeTe$_{1-x}$Se$_{x}$ monolayer films grown on SrTiO$_{3}$. The
superconductivity of the films is robust and rather insensitive to the
variations of the band position and effective mass caused by the substitution
of Se by Te. However, the band gap between the electron- and hole-like bands at
the Brillouin zone center decreases towards band inversion and parity exchange,
which drive the system to a nontrivial topological state predicted by
theoretical calculations. Our results provide a clear experimental indication
that the FeTe$_{1-x}$Se$_{x}$ monolayer materials are high-temperature connate
topological superconductors in which band topology and superconductivity are
integrated intrinsically.
