  This article describes the Silicon Track Trigger (STT) which has been fully
commissioned in 2004 at the DO experiment. The STT allows to enrich already at
the second trigger level the data sample with events containing B-mesons. The
STT achieves this by providing within about 50 microseconds tracks with an
impact parameter resolution of around 50 micrometer. The article shows
preliminary results of the trigger performance and presents a fast
b-identification algorithm for the second trigger level.
