  PtSe$_2$ ultrathin films are used as the channel of back-gated field-effect
transistors (FETs) that are investigated at different temperatures and under
super-continuous white laser irradiation. The temperature-dependent behavior
confirms the semiconducting nature of multilayer PtSe$_2$, with p-type
conduction, a hole field-effect mobility up to 40 cm2/(Vs) and significant gate
modulation. Electrical conduction measured along different directions shows
isotropic transport. A reduction of PtSe$_2$ channel conductance is observed
under exposure to light. Such negative photoconductivity is explained by a
photogating effect caused by photo-charge accumulation in SiO$_2$ and at the
Si/SiO$_2$ interface.
