How can I calculate the junction-to-ambient thermal resistance, R_th(j-a), of a small-signal transistor?

The junction-to-ambient thermal resistance, R_th(j-a), of a small-signal transistor can be calculated from its collector power dissipation as follows:

Equation: R_th(j-a) ＝ (T_j Max - T_a） / P_C MAX

• R_th(j-a): Junction-to-ambient thermal resistance
• T_j Max: Maximum junction temperature
• T_a: Ambient temperature (temperature condition of P_C Max)
• P_C Max: Maximum collector power dissipation