  We construct boson star configurations in quantum field theory using the
semiclassical gravity approximation. Restricting our attention to the static
case, we show that the semiclassical Einstein-Klein-Gordon system for a {\it
single real quantum} scalar field whose state describes the excitation of $N$
{\it identical particles}, each one corresponding to a given energy level, can
be reduced to the Einstein-Klein-Gordon system for $N$ {\it complex classical}
scalar fields. Particular consideration is given to the spherically symmetric
static scenario, where energy levels are labeled by quantum numbers $n$, $\ell$
and $m$. When all particles are accommodated in the ground state $n=\ell=m=0$,
one recovers the standard static boson star solutions, that can be excited if
$n\neq 0$. On the other hand, for the case where all particles have fixed
radial and total angular momentum numbers $n$ and $\ell$, with $\ell\neq 0$,
but are homogeneously distributed with respect to their magnetic number $m$,
one obtains the $\ell$-boson stars, whereas when $\ell=m=0$ and $n$ takes
multiple values, the multi-state boson star solutions are obtained. Further
generalizations of these configurations are presented, including the
multi-$\ell$ multi-state boson stars, that constitute the most general
solutions to the $N$-particle, static, spherically symmetric, semiclassical
real Einstein-Klein-Gordon system, in which the total number of particles is
definite. In spite of the fact that the same spacetime configurations also
appear in multi-field classical theories, in semiclassical gravity they arise
naturally as the quantum fluctuations associated with the state of a single
field describing a many-body system. Our results could have potential impact on
direct detection experiments in the context of ultralight scalar field/fuzzy
dark matter candidates.
