Let
$\sigma $
be a stability condition on the bounded derived category
$D^b({\mathop{\mathrm {Coh}}\nolimits } W)$
of a Calabi–Yau threefold W and
$\mathcal {M}$
a moduli stack parametrizing
$\sigma $
-semistable objects of fixed topological type. We define generalized Donaldson–Thomas invariants which act as virtual counts of objects in
$\mathcal {M}$
, fully generalizing the approach introduced by Kiem, Li and the author in the case of semistable sheaves. We construct an associated proper Deligne–Mumford stack
$\widetilde {\mathcal {M}}^{\mathbb {C}^{\ast }}$
, called the
$\mathbb {C}^{\ast }$
-rigidified intrinsic stabilizer reduction of
$\mathcal {M}$
, with an induced semiperfect obstruction theory of virtual dimension zero, and define the generalized Donaldson–Thomas invariant via Kirwan blowups to be the degree of the associated virtual cycle
$[\widetilde {\mathcal {M}}]^{\mathrm {vir}} \in A_0(\widetilde {\mathcal {M}})$
. This stays invariant under deformations of the complex structure of W. Applications include Bridgeland stability, polynomial stability, Gieseker and slope stability.