  Transistors realized on 2D antiferromagnetic semiconductor CrPS$_4$ exhibit
large magnetoconductance, due to magnetic-field-induced changes in magnetic
state. The microscopic mechanism coupling conductance and magnetic state is not
understood. We identify it by analyzing the evolution of the parameters
determining the transistor behavior -- carrier mobility and threshold voltage
-- with temperature and magnetic field. For temperatures T near the N\'eel
temperature $T_N$, the magnetoconductance originates from a mobility increase
due to the applied magnetic field that reduces spin fluctuation induced
disorder. For $T << T_N$, instead, what changes is the threshold voltage, so
that increasing the field at fixed gate voltage increases the density of
accumulated electrons. The phenomenon is explained by a conduction band-edge
shift correctly predicted by \emph{ab-initio} calculations. Our results
demonstrate that the bandstructure of CrPS$_4$ depends on its magnetic state
and reveal a mechanism for magnetoconductance that had not been identified
earlier.
