Arrange the oven rack to the mid position and preheat oven to 425ºF. Line a baking sheet with enough foil to completely enclose around salmon. Arrange salmon onto the foil-lined baking sheet.
Stir together melted butter, garlic, and lemon juice and pour over the salmon. Sprinkle with salt, pepper and rosemary and enclose the salmon into the foil packet.
Bake the salmon for 12 minutes, then open up the foil packet and turn the oven to the broil setting. Broil the salmon on high for 5 minutes.