On state losses in power BJT:
Transistor have four types of losses one is turn on state losses second is turn off state losses third is turn on switching losses and fourth is turn off switching losses. In off state, the leakage current is in the range of few milliamperes so the off state losses are low as compared to on state losses. High frequency will have high switching losses. The on state losses is determined by saturation voltage between collector and emitter and collector current as Ploss ON = VCE sat x IC
With increasing collector current collector to emitter saturation voltage increases.