We show that the transconductance of multilayer ${\mathrm{WSe}}_2$ field-effect transistors serves as a direct electrical spectrometer of the intervalley relaxation time ${\tau }_{\mathrm{iv}}$, previously accessed mainly by ultrafast optical techniques. Extending an equilibrium valley-thermodynamics framework with a single relaxation equation for the $\mathrm{\Gamma }$-valley carrier fraction $f_{\mathrm{\Gamma }}\left(t\right)$, we predict three signatures: (i) a Lorentzian transconductance $g_m\left(\omega \right)=g_{m,0}+g_{m,v}^0/(1+i\omega {\tau }_{\mathrm{iv}})$, whose imaginary part peaks at ${\omega }_c={\tau }_{\mathrm{iv}}^{-1}$ with opposite signs for bilayer and trilayer; (ii) a two-stage current transient after a gate step, exhibiting bilayer overshoot or trilayer undershoot; and (iii) sweep-rate-proportional hysteresis whose gate-voltage profile and the layer-dependent transconductance sign reversal distinguish valley from trap-induced dynamics. All three signatures provide quantitative electrical access to ${\tau }_{\mathrm{iv}}$ with standard radio-frequency (rf) and direct-current (dc) instrumentation.

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• Electrical conductivity
• Transport phenomena
• Valley degrees of freedom
• Valleytronics
• 2-dimensional systems
• Layered semiconductors
• Semiconductors
• Thin films
• Transition metal dichalcogenides
• Two-dimensional electron system