  We report a strong Kondo effect (Kondo temperature ~ 4K) at high magnetic
field in a selective area growth semiconductor quantum dot. The Kondo effect is
ascribed to a singlet-triplet transition in the ground state of the dot. At the
transition, the low-temperature conductance approaches the unitary limit. Away
from the transition, for low bias voltages and temperatures, the conductance is
sharply reduced. The observed behavior is compared to predictions for a
two-stage Kondo effect in quantum dots coupled to single-channel leads.
