Defect spectroscopy in two-dimensional (2D) field-effect transistors (FETs) requires architectures that minimize contact and disorder-induced artifacts while preserving intrinsic carrier dynamics. We realize ${\mathrm{ReS}}_2\text{−}h\mathrm{BN}$ FETs with few-layer graphene (FLG) van der Waals contacts that form nearly barrier-free interfaces, yielding intrinsic transport with room-temperature mobilities of $18{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$. ${\mathrm{ReS}}_2$, a low-symmetry Group VII transition-metal dichalcogenide (TMD) with weak interlayer coupling, offers a distinct platform to explore defect-transport coupling beyond widely studied TMDs. The low-disorder ${\mathrm{ReS}}_2$-FLG architecture enables detection of random telegraph noise (RTN) even in micron-scale channels, revealing discrete two-level current fluctuations between 90 and 150 K arising from stochastic charge trapping at localized $h\mathrm{BN}$ defect sites. Interestingly, pronounced RTN persists over a broad gate-voltage range, consistent with disorder-dominated percolative transport in the ${\mathrm{ReS}}_2$ channel, where a single trap near a critical bottleneck can modulate the device conductance. With increasing temperature, the RTN evolves into a $1/f$ spectrum as multiple traps activate. Statistical analysis of RTN amplitudes and capture-emission kinetics uncovers defect energetics consistent with substitutional carbon-related centers in $h\mathrm{BN}$. These results establish FLG-contacted ${\mathrm{ReS}}_2\text{−}h\mathrm{BN}$ heterostructures as a sensitive and generalizable platform for probing dielectric-origin defect dynamics and charge trapping phenomena in van der Waals nanoelectronics.

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• Defects
• Electrical properties
• Noise
• Transport phenomena
• Device fabrication
• Devices
• Heterostructures
• van der Waals systems
• Electrical transport techniques