  We have investigated the magnetic properties of highly anisotropic layered
ferromagnetic semiconductor CrI$_3$ in presence of hydrostatic pressure ($P$).
At ambient pressure, magnetization exhibits a clear anomaly below 212 K along
with a thermal hysteresis over a wide temperature range (212-180 K), where a
first-order structural transition is observed. CrI$_3$ undergoes a second-order
ferromagnetic-paramagnetic phase transition with Curie temperature $T_C$=60.4
K. With application of pressure, the transition becomes sharper and $T_C$ is
found to increase from 60.4 to 64.9 K as $P$ increases from 0 to 1.0 GPa. $T_C$
increases with $P$ in a sublinear fashion. The thermal hysteresis in
magnetization and the increase of $T_C$ with pressure suggest that the spin and
lattice degrees of freedom are coupled. The observed increase in $T_C$ has been
explained on the basis of change in inter-layer coupling and Cr-I-Cr bond angle
with pressure.
