For the 2N 338 transistor the manufacturer specifies Pmax

For the 2N 338 transistor the manufacturer specifies P_max = 100 mW at 25ºC free-air temperature and maximum junction temperature, T_jmax = 125ºC. Its thermal resistance is:

Given T_{j man} = 125ºC
T_A = 25ºC
P_max = 100 mW
Q_jc = thermal resistance =?
from the relation

Q_jc =	T_{j (max)} – T_ambient
	P_max

=	125 – 25
	100 mw

=	100	= 1000° C/W
	100 × 10^–3