Glossary/Thermal/Junction temperature

Junction temperature

Junction temperature is the temperature of the semiconductor die itself, the hottest and most safety-relevant reading, always above the package or case temperature.

Also known as Tjunction, Tj, die temperature

Not measurable from a browser

A browser cannot read temperatures, power draw, fan speed, VRAM capacity, clock frequency or native FLOPS. For a direct reading use a native monitor such as HWiNFO64, GPU-Z or lm-sensors. SystemCheck contributes the other half: whether the condition is costing you throughput, measured as decay and consistency.

Sensors sit on the die near the hottest structures, so junction temperature is what firmware compares against TjMax to decide when to throttle. Case or package temperature, measured on the exterior of the chip, always reads lower and is not the number that governs behaviour.

AMD's Ryzen reporting and modern GPU hotspot readings are junction-style measurements, which is one reason those chips appear to run hotter than older parts reporting a package average. They are not hotter; they are reporting a different point.

SystemCheck cannot measure junction temperature. No browser can read any temperature sensor. The web platform deliberately exposes none, both for security and because it would be a strong fingerprinting vector. For junction temperature use HWiNFO64, Core Temp, or Ryzen Master on Windows, or `lm-sensors` on Linux. SystemCheck's contribution is measuring whether the resulting throttling actually costs you performance, which the temperature reading alone cannot tell you.

Related terms

Hotspot temperatureHotspot temperature is the hottest point on a GPU die as reported by its densest sensor, and it is typically 10-20 °C above the reported core temperature.Read more Throttle pointThe throttle point is the temperature at which a chip begins reducing clocks to protect itself, commonly 95-105 °C on CPUs and 83-90 °C on GPUs.Read more Thermal throttlingThermal throttling is a processor reducing its clock speed and voltage automatically once it reaches a temperature limit, to avoid damage.Read more Delta TDelta T is the difference between a component's temperature and the ambient air, and it is the only fair way to compare cooling across rooms and seasons.Read more Thermal decayThermal decay is the measurable fall in performance from the start of a sustained load to its steady state as the system heats and hits its limits.Read more

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