  Epitaxially-grown superconductor/dielectric/superconductor trilayers have the
potential to form high-performance superconducting quantum devices and may even
allow scalable superconducting quantum computing with low-surface-area qubits
such as the merged-element transmon. In this work, we measure the
power-independent loss and two-level-state (TLS) loss of epitaxial,
wafer-bonded, and substrate-removed Al/GaAs/Al trilayers by measuring lumped
element superconducting microwave resonators at millikelvin temperatures and
down to single photon powers. The power-independent loss of the device is $(4.8
\pm 0.1) \times 10^{-5}$ and resonator-induced intrinsic TLS loss is $(6.4 \pm
0.2) \times 10^{-5}$. Dielectric loss extraction is used to determine a lower
bound of the intrinsic TLS loss of the trilayer of $7.2 \times 10^{-5}$. The
unusually high power-independent loss is attributed to GaAs's intrinsic
piezoelectricity.
