You can have maximum current through the transistor and you can have maximum voltage across it but you can't have both at the same time. This is specified in the "safe operating area" power curve.
Figure 1. The safe operating area of a BDV66C transistor. Source: Wikipedia Safe operating area.
In Figure 1 we can see the following:
- 16 A at about 12 V. Pmax = 192 W.
- 5 A at 50 V. Pmax = 250 W.
- 0.2 A at 120 V. Pmax = 30 W.
Taking the two maxima from the graph one might have expected that the device could handle 16 A at 120 V = 1,920 W which is not the case.
SOA is defined as the voltage and current conditions over which the device can be expected to operate without self-damage. The SOA figures are, of course, subject to other constraints such as maximum junction temperature and so the power dissipated as heat, even when inside the SOA, must be conducted away to maintain a safe operating temperature. There is more information in the linked wiki article.