For the $2 \mathrm{N} \; 338$ transistor, the manufacturer specifics $\mathrm{P}_{\max }=100 \mathrm{~mW}$ at $25^{\circ} \mathrm{C}$ free-air temperature and the maximum Junction temperature, $\mathrm{T}_{\mathrm{jmax}{ }^{\prime}}=125^{\circ} \mathrm{C}$. Its thermal resistance is ___________.