We report the characterization of back-gated field-effect transistors fabricated using platinum diselenide (PtSe ) ultrathin films as a channel. We perform a detailed study of the electrical conduction as well as of the photoconductivity. From the gate modulation of the channel current, we obtain the signature of p-type semiconducting conduction with carrier mobility of about 30 cm 2 V −1 s −1 . More interestingly, PtSe devices exposed to light, either in air and in vacuum, exhibit negative

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... oconductivity, which we explain by a photogating effect due to charge trapping in the gate dielectric and light-induced desorption of adsorbates.