What is the SI unit of thermal resistance?

Thermal resistance ($R_{th}$) is defined using the analogy to Ohm's law for heat transfer:

$H = \dfrac{\Delta T}{R_{th}}$

where $H$ is the heat current (rate of heat flow)$and \Delta T$ is the temperature difference.

Rearranging the formula gives:

$R_{th} = \dfrac{\Delta T}{H}$

The SI unit of temperature difference ($\Delta T$) is Kelvin ($\text{K}$).
The SI unit of heat current ($H = \dfrac{\Delta Q}{\Delta t}$) is Watt ($\text{W}$).

Therefore, the SI unit of thermal resistance is $\text{K W}^{-1}$.

Answer: $\text{K W}^{-1}$