  We present a 380-520 GHz balanced superconductor-insulator-superconductor
(SIS) mixer on a single silicon substrate. All radio-frequency (RF) circuit
components are fabricated on a $9 \mu$m thick membrane. The intermediate
frequency (IF) is separately amplified and combined. The balanced mixer chip,
using Nb/Al/Al$_{2}$O$_{3}$/Nb SIS junctions, is mounted in a tellurium copper
waveguide block at 4.2 K using Au beam lead contacts. We find uncorrected
minimum receiver double-sideband noise temperatures of 70 K and a noise
suppression of up to 18 dB, measured within a 440-495 GHz RF and a 4-8 GHz IF
bandwidth, representing state-of-the-art device performance.
