There are two ways to easily determine this: 1. Color: When the salmon is raw or not well cooked, it is got a salmon color and is transparent. When done, the sides of the salmon should be at least opaque and pink. 2. To measure is to know. The core temperature of medium baked salmon (and that's how it really is the best) should be 130 °F (ca. 54 °C). This is measured in the center of the thickest part of the salmon.