Preheat oven to 400°F. Mix salt, garlic powder, pepper, and rosemary in small bowl. Sprinkle evenly over both sides of steak.
Heat cast iron skillet on high heat until hot. Add oil; reduce heat to medium. Sear steak 1 to 2 minutes per side or until browned. Transfer skillet to oven. Bake until steak is desired doneness; about 4 to 6 minutes for medium rare (130°F to 135°F) or about 7 minutes for medium (140°F to 145°F).
Carefully remove pan from oven. Transfer steak to cutting board and let stand 5 minutes. Meanwhile, add butter to skillet on medium heat, stirring until melted. Add red wine. Cook 1 minute, stirring to release brown bits from bottom of pan. Serve red wine sauce with steak.